Don't touch the This pointer after it has been freed.

dlls/shell32/dragdrophelper.c

@@ -122,8 +122,9 @@ static ULONG WINAPI IDropTargetHelper_fnRelease (IDropTargetHelper * iface)
     TRACE ("(%p)->(count=%lu)\n", This, This->ref);
 
     if (!--(This->ref)) {
-	TRACE ("-- destroying (%p)\n", This);
+        TRACE("-- destroying (%p)\n", This);
         LocalFree ((HLOCAL) This);
+        return 0;
     }
     return This->ref;
 }

dlls/shell32/shfldr_desktop.c

@@ -172,6 +172,7 @@ static ULONG WINAPI ISF_Desktop_fnRelease (IShellFolder2 * iface)
 	if (This->sPathTarget)
 	    SHFree (This->sPathTarget);
 	LocalFree ((HLOCAL) This);
+        return 0;
     }
     return This->ref;
 }

dlls/shell32/shfldr_mycomp.c

@@ -177,6 +177,7 @@ static ULONG WINAPI ISF_MyComputer_fnRelease (IShellFolder2 * iface)
         if (This->pidlRoot)
             SHFree (This->pidlRoot);
         LocalFree ((HLOCAL) This);
+        return 0;
     }
     return This->ref;
 }