A Jbutton does not get an mouse exit event.
The situation occurs in a number of situations
  - Another Frame borders the button
  - the mouse does not move, but the frame is being moved
      underneath the mouse
  - Frames are being pushed in the background

The problem occurs on all platforms (Windows & Solaris)
The problem can be recreated by the following example
in a Solaris 8 CDE environment:

1.) Compile file RolloverBug.Java and start it with $ java RolloverBug
    A frame will show up with a green button with the text "rollover FALSE"
2.) Place any oher frame (dtterm for example) over the "Rollover Bug" frame
that it will hide the lower half of the button
3.) Move the mouser around both windows ro the top of the screen
and start moving down. The following will happen
a.) The button will turn red as soon as the mouse enters the button
area from the top
b.) The button color should turn green as soon as the mouse enters
the space of the secondary frame (for example dtterm Windows).
This is the error situation!
The button should turn green again.
This is not happening.

Second example:
1.) Start application like in first example
2.) Move the application over another CDE Window.
3.) Have focus on Java application
4.) Move mouser over button (button turns red)
5.) Push Window with ALT F3 into backhround
==> Window is now hidden.
6.) Uncover Java application by moving upper frame aside
==> Button becomes visible. It still red (no event received)