Run Scrivener 2.5 on Mavericks, tick “Use secondary screen if available” under composition mode settings. Open scrivener in full screen mode on secondary screen and then activate composition mode. Then exit composition mode and then exit fullscreen mode. You’ll find that the menubar on the screen on which Scrivener was open in fullscreen mode has disappeared. It can be recalled as if in fullscreen mode, but on the screen on which composition mode appeared.
I can see that you may not consider this to be a bug since the setting applies to the secondary screen. However, this did not happen on Mountain Lion, so it’s worth mentioning.
Thanks for the report, I’ve added it to the list for investigation. I can’t promise anything, given that it’s new Mavericks behaviour, but I’ll definitely look at what is going on.
I have found a workaround for this. If you close composition mode, drag the fullscreen app to the primary display, and then exit fullscreen mode, the menubar behaves as it should.
I thought I should report that this behaviour has worsened on 10.9.3. If Scrivener is in Fullscreen mode on my laptop display and composition mode on my external display, when I exit Composition mode and then Fullscreen mode, I am not able to summon the menubar at all. Also, now when I use composition mode when it is set to open on a different display and Scrivener is NOT in fullscreen mode on my laptop display, I lose the menubar on the laptop side until I exit composition mode.