Has it been clearer? If not, why is that?
PS: why is that question (which is now clearer) still bad?
why is that question (which is now clearer) still bad?
While you have improved the question, the underlying question still cannot be answered by the community. You basically want to know the reason the developers of
PDF-XChange Viewer, used a GUI element that behaves the way you describe.
While I could guess the reason, the control (bookmark panel) works the way it does, without the source code to the entire program I couldn't tell you the actual reason. While some community members, yourself included might get some benefit from an answer which simply guesses the reason something is the case, most community members wouldn't agree with that conclusion (myself included). I personally find answers based on assumptions to be unhelpful.
At the end of the day, knowing the reason the control works the way it does, won't change how it works. This isn't something that can be modified. It isn't clear what problem would be solved by knowing the reason, the bookmark panel, behaves the way it does.