Version idea from the 9th appeared not very nice bug.
In the project's view disappears before plus the package containing the classes
What is strange packages always the same.
After the folding / unfolding of the parent node (in my case, the node src) plus reappears.
This happens in all versions 9.x
Who's watching something that you like?
Registered BUG http://youtrack.jetbrains.net/issue/IDEA-52750
but I am afraid that this is my personal bug.