Bad layout of clef when added to first note of system

Ubuntu Studio 14.04, GIT commit: 5373c93

This was originally reported as #3 within #28826: Wrong clef at start of system, but since the other symptoms there are fixed, and this does seem unrelated, I'm filing it separately. I also have somewhat more reliable to reproduce

1) new score, 32 measure
2) fill first six measures with notes
3) add line break after measure 4
4) drag bass clef to first note of measure 5 (beginning of second system)

This clears itself up after a reload, or after any operation that causes system layout to change. To reproduce this, it's important you use drag and not double click; it's also important you release on the first note rather than on the measure as a whole.

For the record, here were the original steps - we should make sure any fix also works for this case:

1) new score, 32 measures, set page size to Letter
2) fill first twelve measures with quarter notes
3) drag (don't use click / double-click) alto clef to first note of measure 9 (last measure of first system)

Result: clef for second system appears just above the clef for the *third* system: