1.6.1 build 1665 - The right side and bottom scroll bars sometimes disappear

Hi,
I just updated to the subject version and I noticed when viewing image, the scroll bars on the right and bottom side disappear sometimes.  My apologies for the "sometimes", but I haven't figured out exactly what I am doing when this happens.
Jim
P.S.  I think I just figured out what I was doing when this happens.... It is when I use my mouse to drag the image that is being viewed.. then the scroll bars disappear.
P.P.S.  Sorry again - the behavior (dragging ==> scrollbars disappear) doesn't seem to be consistent, i.e., sometimes when I drag, the scrollbars disappear, and sometimes when I drag, the scrollbars don't disappear.