Colliding actions on ProgressPanel ? NullPointerException in "AWT-EventQueue-0"

My CMD window shows exceptions like this from time to time when certain activities (e.g. opening the partner window) are being performed in the AS2 GUI:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.desktop/javax.swing.plaf.basic.BasicProgressBarUI.sizeChanged(Unknown Source)
at java.desktop/javax.swing.plaf.basic.BasicProgressBarUI.setAnimationIndex(Unknown Source)

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.desktop/javax.swing.plaf.basic.BasicProgressBarUI.updateSizes(Unknown Source)
at java.desktop/javax.swing.plaf.basic.BasicProgressBarUI.getBox(Unknown Source)

As far as I was able to find out, this is likely connected to Swing not being "thread safe" and multiple threads accessing Swing/AWT components in parallel.
In my further investigation, I looked up the source code for class "de.mendelson.util.ProgressPanel".

Method "displayProgressBar" makes use of "SwingUtilities.invokeAndWait" ... which is good and "as recommended", I think.
On the other hand, method "disableProgressDisplay" does not use "invokeAndWait" or "invokeLater".

Shouldn't "disableProgressDisplay" enqueue its GUI related commands to the Swing eventqueue as well ?

... since the same Swing/AWT components ("jProgressBar" and "jLabelProgressDetails") are affected as in "displayProgressBar".
... and since "disableProgressDisplay" is executed in separate threads as well. (... via "stopProgressIfExists", as initiated from class AS2Gui)