Index: /CKEditor/trunk/_source/plugins/tabletools/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/tabletools/plugin.js	(revision 4840)
+++ /CKEditor/trunk/_source/plugins/tabletools/plugin.js	(revision 4841)
@@ -370,7 +370,12 @@
 		// 2. In solo mode while not exactly only one selected.
 		// 3. Cells distributed in different table groups (e.g. from both thead and tbody).
-		if( ( mergeDirection ? cells.length != 1 : cells.length < 2 )
-			 || selection.getCommonAncestor().is( 'table' ) )
+		var commonAncestor;
+		if ( ( mergeDirection ? cells.length != 1 : cells.length < 2 )
+				|| ( commonAncestor = selection.getCommonAncestor() )
+				&& commonAncestor.type == CKEDITOR.NODE_ELEMENT
+				&& commonAncestor.is( 'table' ) )
+		{
 			return false;
+		}
 
 		var	cell,