If you've tried it in (say) kwin and icewm and got the same result, it's probably a problem with the way Impress talks to WMs rather than any WMs getting things wrong.
So both these windows are on the same display, yet the presence of the second display causes the problem? That's pretty bizarre. I don't have a dual-head display to test on, though. I hope someone who knows about Impress will be along soon.
If you've tried it in (say) kwin and icewm and got the same result, it's probably a problem with the way Impress talks to WMs rather than any WMs getting things wrong.
So both these windows are on the same display, yet the presence of the second display causes the problem? That's pretty bizarre. I don't have a dual-head display to test on, though. I hope someone who knows about Impress will be along soon.