http://java.net/jira/browse/MACOSX_PORT-770 submitted 2011/12/08 by Yuri Nesterenko
In the test attached to the issue 769 apply workaround (setPreferredSize to the scoll pane) and run it couple of times. It will fail, by the way. Look at the amount of empty space in the scroll bar; after removing and re-adding of the scroll pane content it gets someway smaller.
I'm not sure also it is painted correctly.
Consider rising priority here.