Corruption after failed delete of time signature

Ubutnu 14.04, GIT commit: b4b5e28

Similar to but different from #51216: Corruption after failure to change time signature

1) new score, 3/4
2) add 4/4 to measure 2
3) measure 2 note entry: 6 Ctrl+3 C D E (quarter note triplets) F G (quarter notes)
4) copy measure 2 to measure 3 & 4
5) select 4/4 time sig
6) delete

Result: dialog warning of tuplet crossing, which is correct. But on hitting OK, the time signature was deleted anyhow, leaving corrupt measures behind.

We need to restore the time signature we prematurely deleted.