On the surface, this error report may appear quite bizarre, but I have
spent a lot of time narrowing-down the conditions that trigger the
problem.

Since Ubuntu 16.04 came out in April, I have been seeing the yellow
notes, but have been unable to identify what triggered them.  I finally
spent a lot of time trying to narrow down the trigger, and this is what
I have come up with.

A few additional points may be useful to consider:

1. You have to actually scroll the combo-box.  If you just expand the
combo-box, and select anything within the range displayed, the problem
does not occur.

2. Even if you scroll a combo-box in another pane (such as the "F1 Help
/ Setup" pane's "Configuration Files" combo-box), it will affect all the
other tabbed-panes.

3. Although the "Instrument" combo-box being scrolled will trigger the
problem on many machines, it would not trigger the problem on all of my
test machines.  Only the "ASSIGNABLE" slider's combo-box (and the
"Configuration Files" combo-box on the "F1" pane) will trigger the
problem on all of my test machines.

4. Although the "ASSIGNABLE" slider's combo-box has both an Action-
Performed and State-Change listener, the only action taken by those
listeners is to log the event using System.out.println().  The
configuration files combo-box, on the other hand, has a lot of side-
effects.

5. It may seem far-fetched that a component in a separate panel can affect the 
graphics in an adjacent panel, but I can point out cases you can reproduce 
(bugs I have been living with for a long time without reporting) where this is 
definitely the case.  For instance, if you hit a key to produce a note 
immediately to the left of one of sliders (holding it down so the dot remains 
displayed), and while doing so, manipulate the slider to the right of the note 
using the mouse, the note-dot gets erased, even though the key producing the 
note is left down (and the note's sound continues audibly). This problem has 
been observed in openjdk-7, and on Oracle Java as well.  I can submit a problem 
report for that if you wish.  
 
I will attached a text-file containing the System.out.println() entries in the 
area where the problem occurred.  I did not observe anything out of the 
ordinary for cases with the yellow notes.

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https://bugs.launchpad.net/bugs/1611180

Title:
  JPanel XOR Graphics Is Wrong Color After Scrolling A Combo-Box

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