the property change is fired only if the animated property is true. This forces client
code to add different logic for both if they need to do stuff (like re-sizing the containing
top level window) when the collapse is really done.
Thinking about it: isn't "collapsed" fired incorrectly? Arguable of course - but one (my
pov might be that a property change must be fired only after all internal state
is updated, that is at the end of the animation period.
added test method to JXTaskPaneIssues (too lazy to re-formulate for a bare JXCollapsiblePane)