Crash in void QGraphicsScene::clear()

the small appended program crashes when you do the following:

• compile it with VS 2008, SP1 on WINDOWS XP, SP3 using Qt-4.6.0-rc1
• start it
• press the shortcut key "A" to activate the slot-function
  "moveToBackground"
• close it

it crashes in the line "delete d->topLevelItems.first();" while trying to
use an already deleted item.