diff --git a/src/gui/interact/ui-coord-resolver.hpp b/src/gui/interact/ui-coord-resolver.hpp
index f7b901498..5abc497bc 100644
--- a/src/gui/interact/ui-coord-resolver.hpp
+++ b/src/gui/interact/ui-coord-resolver.hpp
@@ -322,7 +322,6 @@ namespace interact {
               res_.depth = res_.covfefe->size();
               this->uic_ = std::move (*res_.covfefe);
               res_.covfefe.reset();
-              ENSURE (isCovered());
             }
           else
             {
@@ -331,6 +330,7 @@ namespace interact {
               REQUIRE (not res_.covfefe);
               truncateTo (0);
             }
+          ENSURE (isCovered());
           return std::move (*this);
         }
       
@@ -366,7 +366,6 @@ namespace interact {
           ENSURE (isCovered());
           append (pathExtension);
           res_.depth = query_.determineCoverage (this->uic_); // coverage may grow
-          ENSURE (isCoveredPartially());
           return std::move (*this);
         }
       
@@ -374,27 +373,28 @@ namespace interact {
       extend (UICoord const& partialExtensionSpec)
         {
           if (not canCover())
-            {
-              uic_ = partialExtensionSpec;
-            }
+            uic_ = partialExtensionSpec;
           else
             {
-              ENSURE (res_.isResolved and res_.covfefe);
-              size_t coverable = res_.covfefe->size();
+              REQUIRE (res_.isResolved);
+              size_t coverable = res_.covfefe? res_.covfefe->size() : res_.depth;
               auto newContent = partialExtensionSpec.begin();
               size_t extensionPos = newContent? partialExtensionSpec.indexOf(*newContent) : 0;
               if (coverable >= extensionPos)
                 throw error::Invalid (util::_Fmt{"Attempt to extend covered path %s with %s "
                                                  "would overwrite positions %d to %d (incl)"}
-                                                % *res_.covfefe
+                                                % (res_.covfefe? *res_.covfefe : UICoord{uic_.rebuild().truncateTo(res_.depth)})
                                                 % partialExtensionSpec
                                                 % extensionPos
                                                 % coverable);
               cover();
               for ( ; newContent; ++newContent, ++extensionPos )
                 overwrite (extensionPos, *newContent);
+              normalise();
             }
-          res_.depth = query_.determineCoverage (this->uic_); // coverage may grow
+          res_ = Resolution{};      // start over with pristine resolution state
+          attempt_trivialResolution();
+          canCover();
           return std::move (*this);
         }
       
diff --git a/src/gui/interact/ui-coord.hpp b/src/gui/interact/ui-coord.hpp
index 0ad6b43c9..5c6675ba2 100644
--- a/src/gui/interact/ui-coord.hpp
+++ b/src/gui/interact/ui-coord.hpp
@@ -158,6 +158,7 @@ namespace interact {
       Builder path (Literal pathDefinition) const;
       Builder append  (Literal elmID) const;
       Builder prepend (Literal elmID) const;
+      Builder rebuild() const;
       
       
       
@@ -711,6 +712,12 @@ namespace interact {
     return Builder(*this).prepend (elmID);
   }
   
+  inline UICoord::Builder
+  UICoord::rebuild ()  const
+  {
+    return Builder(*this);
+  }
+  
   
   
 }}// namespace gui::interact
diff --git a/tests/gui/interact/ui-coord-resolver-test.cpp b/tests/gui/interact/ui-coord-resolver-test.cpp
index f27bffef6..cf5480db2 100644
--- a/tests/gui/interact/ui-coord-resolver-test.cpp
+++ b/tests/gui/interact/ui-coord-resolver-test.cpp
@@ -634,18 +634,24 @@ namespace test {
           
           /* === extend fully covered explicit path === */
           UICoordResolver r1 {UICoord{"window-2","persp-B","panelY"}, tree};
-          r1.extend (UICoord().path("engulfed"));
+          r1.extend (UICoord().path("gappy").tab(2));
+          cout << string(r1)<<endl;
+          r1.extend ("seamless");
           cout << string(r1)<<endl;
           
           /* === extend partially covered path === */
           UICoordResolver r2 {UICoord().view("thirdView").append("some/where"), tree};
           r2.extend ("no/where");
+          cout << string(r2)<<endl;
           VERIFY_ERROR (INVALID, r2.extend(UICoord().persp("fisheye")));
           cout << string(r2)<<endl;
           
           /* === unsolvable: truncate, extend, recalculate coverage === */
           UICoordResolver r3 {UICoord().persp("awesome"), tree};
-          r3.extend (UICoord::currentWindow().view("outlandish"));
+          CHECK (not r3.canCover());
+          CHECK (0 == r3.coverDepth());
+          r3.extend (UICoord::currentWindow().tab(1));
+          CHECK (1 == r3.coverDepth());
           cout << string(r3)<<endl;
         }
     };
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index e64d5a706..756baad95 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -8936,21 +8936,24 @@
 </node>
 </node>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515451105808" ID="ID_1323377531" MODIFIED="1515451115328" TEXT="extend">
-<icon BUILTIN="pencil"/>
+<node COLOR="#338800" CREATED="1515451105808" ID="ID_1323377531" MODIFIED="1515460214743" TEXT="extend">
+<icon BUILTIN="button_ok"/>
 <node COLOR="#338800" CREATED="1515451117055" ID="ID_602743049" MODIFIED="1515451126326" TEXT="durch explizit gegebenes Suffix">
 <icon BUILTIN="button_ok"/>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515451127221" ID="ID_130067342" MODIFIED="1515451168209" TEXT="durch (partielle) UI-Coord spec">
+<node COLOR="#338800" CREATED="1515451127221" ID="ID_130067342" MODIFIED="1515460212289" TEXT="durch (partielle) UI-Coord spec">
 <linktarget COLOR="#4f6f95" DESTINATION="ID_130067342" ENDARROW="Default" ENDINCLINATION="544;89;" ID="Arrow_ID_992203487" SOURCE="ID_1736775031" STARTARROW="None" STARTINCLINATION="704;0;"/>
-<icon BUILTIN="flag-yellow"/>
-<node CREATED="1515455194222" ID="ID_1550640486" MODIFIED="1515455202609" TEXT="brauche (nun doch) overwrite">
+<icon BUILTIN="button_ok"/>
+<node CREATED="1515455194222" ID="ID_1550640486" MODIFIED="1515460223240" TEXT="brauche (nun doch) overwrite">
+<icon BUILTIN="yes"/>
 <node CREATED="1515455204572" ID="ID_538708318" MODIFIED="1515455215023" TEXT="im UI-Coord-Builder ansiedeln"/>
 <node CREATED="1515455215779" ID="ID_1744879837" MODIFIED="1515455225131" TEXT="protected....">
 <icon BUILTIN="smiley-neutral"/>
 </node>
 </node>
-<node CREATED="1515455238808" ID="ID_1864948105" MODIFIED="1515455247459" TEXT="Fehlerbehandlung: &#xdc;berlapp finden"/>
+<node CREATED="1515455238808" ID="ID_1864948105" MODIFIED="1515460226143" TEXT="Fehlerbehandlung: &#xdc;berlapp finden">
+<icon BUILTIN="yes"/>
+</node>
 </node>
 </node>
 </node>
@@ -9368,10 +9371,10 @@
 <icon BUILTIN="flag-yellow"/>
 <icon BUILTIN="button_ok"/>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1506984645748" ID="ID_768385613" MODIFIED="1506984662154" TEXT="verify_mutateExtend">
-<icon BUILTIN="flag-yellow"/>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515449655380" ID="ID_1282321814" MODIFIED="1515449740717" TEXT="expliziten Pfad erweitern">
-<icon BUILTIN="flag-yellow"/>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1506984645748" ID="ID_768385613" MODIFIED="1515460236134" TEXT="verify_mutateExtend">
+<icon BUILTIN="pencil"/>
+<node COLOR="#338800" CREATED="1515449655380" ID="ID_1282321814" MODIFIED="1515460194102" TEXT="expliziten Pfad erweitern">
+<icon BUILTIN="button_ok"/>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515450991631" ID="ID_1736775031" MODIFIED="1515451168209" TEXT="Pfad durch partielle UI-Coord erweitern">
 <arrowlink COLOR="#4f6f95" DESTINATION="ID_130067342" ENDARROW="Default" ENDINCLINATION="544;89;" ID="Arrow_ID_992203487" STARTARROW="None" STARTINCLINATION="704;0;"/>
@@ -9387,6 +9390,12 @@
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515455296784" ID="ID_957569216" MODIFIED="1515455313258" TEXT="sinnvolle Fehlermeldung">
 <icon BUILTIN="flag-yellow"/>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515456807297" ID="ID_940232878" MODIFIED="1515456829799" TEXT="ausgehend von expliziter Spec">
+<icon BUILTIN="flag-yellow"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515456817248" ID="ID_631326169" MODIFIED="1515456828903" TEXT="ausgehend von berechneter Coverage-L&#xf6;sung">
+<icon BUILTIN="flag-yellow"/>
+</node>
 </node>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1515449669446" ID="ID_1747646759" MODIFIED="1515449741572" TEXT="partially covered erweitern">