I am launching Java2Demo with Nimbus LAF flag and doing the following -
1. Go to Transforms Tab.
2. Double click on the transformations happening on the bottom of the screen.
3. Transformations tab enlarges to occupy the full demo area.
4. Choose 'Texture' checkbox and choose the 'green' texture
5. Now move the mouse over the tabs as shown in the screen shot.

You will notice that transformations are now jumpy as you keep moving the mouse in and out of the tabs. I reproduced it on WinXP - 6u12-b03 - Nvidia GeForce 7600 - HW accel disabled. Also reproducible with 6u11 and hence not a regression in 6u12.

I have attached a screenshot that shows the state of different controls on the screen.
Also reproducible with jdk6u10-b33. Reproducible on SolSparc10 as well. Changed the release value to 6u10 in SR.