Multi-measure rest loses clef and key signature on edit (until 'Save')

I have a score with multi-measure rests. I have turned multi-measure rests on, and have noticed a weird behavior:

If the multi-measure rest starts a line (as in first attached screen shot), and then I make an edit (as in second screen shot, where I have inserted a flat), the clef and key signature disappear!

But here is the weird part: If I Save the score, the problem disappears (as in the third screen shot)