as determined by SkinMemoryLeakTest (remove line 165) and a leak tester
https://github.com/andy-goryachev-oracle/Test/blob/main/src/goryachev/apps/LeakTest.java

Make sure to configure the current test in LeakTest:
protected final Type WE_ARE_TESTING = Type.BUTTON_BAR;


caused by:
- adding and not removing listeners
- adding and not removing children Nodes