I have added a vertical scrollbar to a frame to it's east and I have set the unit increment to 1. This is the only component added to the frame. When I click the down arrow, the thumb starts moving. When I keep the down arrow pressed, I could see lot of flickering and at some point, the thumb actually vanishes and the entire scrollbar track grays out. Same flickering is seen during block increment also. It looks pretty bad.

This is reproducible on XToolkit since Mustang-b55 and not reproducible on Mustang-b42. Hence it is a regression introduced somewhere inbetween b42 and b55. Same code works perfectly fine on b42. Works fine on Motif, Win32. I reproduced it on SolSparc10-JDS.

I have attached a sample test. Execute the sample test on SolSparc10-JDS. You would see a frame with a scrollbar. Click the down arrow of the scrollbar (located at the bottom end) and keep it pressed. You would see the bubble of the scrollbar actually vanishing and scrollbar being grayed out.
Same kind of flickering is seen with AWT Choice also. Similar to scrollbar, this is not reproducible with b42 but reproducible with b55. When you click on choice, the drop down appears. Try moving the cursor using the arrow keys and keep the down arrow key pressed. You would actually see the actual Choice component flickering very badly when the selection changes in the drop down. I have attached a choice test as well.
The flickering mentioned in this bug is seen with Checkbox also and it is highly noticeable when changing the fonts/size of the checkbox. Checkbox works fine on b42. Hence I think the root cause of flicking of all these components must be the same. Sample test attached. Try clicking on any of the checkboxes repeatedly.