Alt+Mnemonic stops working for JTabbedPane once the Tooltip with huge text gets displayed.

If the size of the text is sufficient to get displayed within the frame, it's working fine.
 
Find attached test case with the bug report.

To Reproduce the bug :

1) Compile and run the attached Java File.
2) It's an automated one.
* First the ToolTip text is small enough to get displayed within the frame. So it traverses the tabs using Alt+Mnemonic key generation.
* Next, the Tooltip text has been changed to set huge text, so that its display size is greater than the frame size. Now it stopped traversing the tabs with Alt+Mnemonic key generation.