To reproduce this bug, run the "demobrowser" that comes with Qt in debug mode on Windows.
Select the "Inspect" menu option and close the WebInspector that pops up.
Now close the web page that was inspected. It crashes with an access to an already deleted object.
(it needs to be on Windows and in debug mode, otherwise accessing deleted objects does not result in a crash but undefined behaviour instead)
I verified that this was already fixed on the trunk, it just did not make it into Qt 4.6.1.
It is a dubplicate of bug 31664, as far as I can see.
*** This bug has been marked as a duplicate of bug 31664 ***