to prevent forthcoming confusion:
the backtrace in comment #10 refers to the "kwin crashes when a window gets lost while tabbox+compositing" while thi bug is actually about apps crashing somewhere in QDragManager which get's irritated by (likely) fullscreen composite FX
the relation is that
a) the app segfaults for dnd during the fullscreen FX
b) it in consequence gets lost from the tabbox list and causes a segfault in KWin
to prevent forthcoming confusion:
the backtrace in comment #10 refers to the "kwin crashes when a window gets lost while tabbox+compositing" while thi bug is actually about apps crashing somewhere in QDragManager which get's irritated by (likely) fullscreen composite FX
the relation is that
a) the app segfaults for dnd during the fullscreen FX
b) it in consequence gets lost from the tabbox list and causes a segfault in KWin
still independent bugs, though