'invalidComponents' is a List (always ArrayList) field in 'javax.swing.RepaintManager'.
There is an inconsistency in what equality operation is used when searching for an element in the list.
The 'addInvalidComponent' method uses ==.

            int n = invalidComponents.size();
            for(int i = 0; i < n; i++) {
                if(validateRoot == invalidComponents.get(i)) {
                    return;
                }
            }

The 'removeInvalidComponent' method uses equals.

            int index = invalidComponents.indexOf(component);
            if(index != -1) {
                invalidComponents.remove(index);
            }

It can lead to unexpected results, when component overrides 'equals'.