map: The fix for #449285 was buggy and broke display of parents in certian circumstances.

map: The fix for #449285 was buggy and broke display of parents in certian circumstances.

The use of $dummy was not sufficient, because it only stuck around for the
first element after a dummy parent, and was then lost. Instead, use a
$addparent that contains the actual dummy parent, so it can be compared
with the new item to see if we're still under that parent or have moved to
another one.