Comment 7 for bug 870693

"Think of it this way: should a button NOT be shown because it's not immediately clickable? "

Well . . . in this context . . . yes! Afterall, this is the approach that ubuntu developers took with the Global/Application Menu. The current design of the scrollbar makes it difficult to gain control over the Thumb. Appearance of the Thumb coinciding with clickability would address this issue.

I disagree with you that it is a valid/useful reason for the Thumb appearing even when not clickable solely "to tell people that option is there." This is a case where the usability is hurt too much just "to tell people that option is there." Therefore, people will just have to learn that the Thumb only appears when clickable. Besides, once users learn that, the necessity of communicating that the option is there is removed. Again, same thing with the Global/Application Menu.

Considering the problem you faced with Rhythmbox, it's likely not appropriate to put the Thumb inside unmaximized windows. I'm glad you left your experience cause I have not experienced the problem you faced so was not aware of it. And I do hate it when something pops up over what I'm trying to do, so I share your grievance. However, I still think bug 870714 would be a very useful improvement.