Build 2051 on Mac OS X 10.6
Open a short file that doesn't "require" a scroll bar. (That is, the scroll bar appears to span the entire height of the pane.)
Attempt to drag the scroll bar. (Either up or down-- it doesn't matter.)
This causes the pane to "scroll" past the end of the document, such that the entire document is above the viewport. At this point, it looks like the scroll bar is in an inconsistent state. It is at this point not possible to view the document any further since the entire document is out of the viewport, and although you can continue to perform edits, the scroll bar malfunctions from this point on and you can no longer use it until you close and re-open the buffer.
I have not tested later dev builds with the different scrolling behavior, and I do not have "smooth scrolling" turned on.
Customer support service by UserEcho