unstable key signature

I'm writing a piece for orchestra. The current movement is in E major, which puts two clarinet parts and a bass clarinet in F-sharp major, 6 sharps. Obviously this is no big deal, but for some reason Mscore keeps changing the F-sharp major signature to G-flat major, 6 flats. I'd just leave it in G-flat, only it's a fairly chromatic piece, and the transferring from sharps to flats leaves the clarinet parts a considerable mess.

My solution is simple -- I just change the clarinet parts back to F-sharp whenever they flip over to G-flat and keep going. But it's happening frequently and is getting to be quite boring. Does anyone have a quick method for freezing a key signature in place?

(This is not a major problem, I know -- I love Mscore and promote it around here endlessly.)