Also, it happened with many different versions of Hijack installed.

We've already determined that it's not caused by or related to Hijack, as Doug Burnside gets the same lockup on a pure-stock player.

What I found interesting is that the bug managed to interrupt Hijack's ability to repaint its "Done" window without interrupting Hijack's ability to serve web pages. I thought that might give a clue as to the source of the bug.