So in 2003, I reported Bug #123796 in the GNOME bug tracking system. Three years later it was marked as duplicate of Bug #340180. Finally over 3 years after that (today), it was marked as confirmed.
It’s a relatively simple bug, easy to reproduce, and while not a huge important bug, it’s annoying and I’d say at least one out of ten people with dual monitors has probably come across it at some point. Yet it’s sat mostly ignored in the GNOME bug database, as have most of my other reported bugs.
Ah well, I guess there’s a chance that it will be fixed now, should someone step up and actually fix the code that is.