I think the bug I resolved (I wouldn't say fixed) in 
@novelwriter today is the weirdest I've encountered so far.
The app uses @-based keywords to set meta data in the text. An auto-complete menu pops up to suggest which keyword when you type an @ on a new line.
In the current version (at least) if you have the editor "justified margins" set, type an @, then type backspace, then *and only then* will Qt/PyQt segfault and crash the app.