http://bugs.winehq.org/show_bug.cgi?id=29496
--- Comment #3 from David davidsboogs@gmail.com 2012-01-05 14:40:25 CST --- This does not depend on Steam changing tabs, or having just loaded. (Although it is perhaps more frequent in those cases.
There is a second symptom that I have (I think always, but I'm not sure) seen attached to this bug: When the mouse button is released and it Steam doesn't notice, the window or border moves around double the distance from the starting point as the mouse pointer had moved - which explains the "but the cursor will move itself to above the Steam window" - it can happen in any direction though, and when resizing too.
The double movement thing used to be tracked in bug 24579 but it was determined that current behavior (being linked to the mouse not releasing) was different enough to count as a different bug.