If my memory doesn't cheat me, someone else already got the same problem.
Sometimes the pop-up doesn't show up when I hover the mouse on the blue strip in the left bar.
I mean the pop-up that resumes the clef, key etc. etc.
Clicking is ignored.
Double clicking selects the whole staff.
Clicking the right button pops up the local menu as usual.
I found no way to "stimulate" the pop-up beside closing and reopening the whole program.
This happens for all the staves and all the open scores.
As I said, the only way is to close and reopen the program.
I think that you mean the tooltip (http://www.techterms.com/definition/tooltip). I have not experienced this problem.
Yes, that's it.
Sorry.
N.B. Please note the sometimes. I found no way to reproduce it at wish.
This happens to me a lot. In fact, I just noticed that my current NWC instance had the problem right now! When it happens, tooltips still work fine in other apps (e.g. WordPad). Only thing I've found to clear it is to simply close and re-open the NWC instance.