In short, I have this issue when clicking on a file in the project tree do not open the file anymore in my plugin.
What caused this: I replaced the DefaultTreeUI component by my version of TreeUI. To make sure I won't be missing any features of the DefaultTreeUI I copied-pasted the DefaultTreeUI methods, replacing only what I need to replace.
However I still have this issue, even after reverting all my changes, and just using DefaultTreeUI methods. I suspect there is some part in the code that assumes that there can only by a DefaultTreeUI component. Can someone help me figure out this?