Trying to port an old test, I tried it on OS X and found a new bug.
Start the attached code on Mac (I used OS X 10.9).
Move the mouse pointer to the vertical scrollbar outside of thumb (to the so called gray area; everything is gray on Mac but you understand). Press 1st button and keep it pressed.
The content of scrollpane will scroll, and thumb stops by the pointer.
Don't release the button but move the pointer a couple of times up and down along the scrollbar, stopping now and again.

Now, chances are big that the thumb and the scrollpane content start oscillating fast; if you are lucky and stop the pointer in just the right place, this oscillating will be fast AND endless.

I didn't try many native applications but Terminal didn't scroll that way.

An end user may well run into this.
Reproduced on jdk8b132 as well.
Reproducible on Aqua only (on other LaFs the thumb doesn't follow mouse backward move).