Steam doesn't work well with pointer focus, duplicate of #6.
Will this issue be remembered if/when #6 is fixed? (since they are similar bugs but might not completely overlap)
It's really the same underlying issue: the Steam GUI framework triggers a bunch of behaviors on focus changes and it just doesn't play well with pointer focus.
Nothing extracted yet.
When moving the mouse between Steam windows (with Focus-Follows-Pointer enabled) with one of Steam's modal dialogs open, it makes bell noises.
http://youtu.be/tdypcnuRRkY