Sometimes (but not very often), when I'm moving my mouse over a window, it goes transparent. I can't find a way of making it opaque again, and the only recourse is to close that window and open another one.
This happens most often with xfce-terminal, but I've also seen it happen with emacs, so it's probably not related to xfce-terminal itself. These two are the apps I use most of the time, so it's likely they'd be the ones to show the effect.
It's possible that I'm pressing a key or a mouse button at the same time: I'm not aware that I've been doing either, but you never know. Other open windows in the same workspace are not affected.
Anyone else seen this effect? I don't know whether it's a bug or a feature; if it's the latter, is there a key/mouse sequence to turn it off again?
(I have to say that I can't understand why anyone would want a transparent terminal window, but each to his own, I suppose).
Does it happen when your near the Titlebar? If you accidentally move your mouse wheel while over the title it'll set the opacity with scrolling.
Just a thought