Bad key signature insert on switch to concert pitch after inserting measures

1) new score for Bb clarinet, key of Eb, 4/4, 8 measures
2) append measures until it spill over onto a second system
3) disable concert pitch

Result: spurious key change appears at or around the system break

Depending on exactly how things layout, it might be right at the break (with a courtesy signature on first system) or it might show on next measure like this. Further attempts to add or remove measure, or undo/redo, can give you more and more badly transposed keys.

I'm guessing the concert pitch button now needs to be taught about disable key signature segments. I swear I'm not going out of my way looking for these! With any luck it's as easy and safe a fix as #280366: Volta laid out incorrectly in measure with disabled header segments; will followup...