Changing to enharmonic key signature reverts automatically
To reproduce the issue, create a score with an alto Sax and apply the Key of E major to it. You will get the key of C# Major as expected.
Change to the key of Db, following the instructions in the how to at https://musescore.org/en/node/260491
Press the concert pitch button twice and the key signature is back to C#.
If you have a C instrument in the score also, unneeded key signatures are inserted where there were system breaks before pressing concert pitch twice. I saw this when I started with a blank score using letter sized paper.
One other thing. at the end of the first line on the sax, there is a courtesy C natural key signature and it is acutally applied to the part.
This is marked major because there is no workaround.