inserting measure and change time signature
1) create a new score starting with some time signature, for example 3/4
2) fill some measures with notes
3) in the next measure change time signature, for example to 4/4
4) fill one measure with notes
5) in the next measure change time signature ti 5/4
6) fill sime measures with notes
7) again change next measure to 4/4, put some notes
8) go to the measure where started with 5/4
9) insert a new measure before the selected measure
10) try to change time signature in the new inserted measure; in this moment you will already have a mess
11) try to change time signature in the measure which was selected before insertion; a mess becomes even bigger
12) try to get that the new inserted measure be the last in the system (before breaking in the new system), and change time signature ...
... and so on. I have seen different strange effects: the time signature were duplicated ..., when trying to change time signature in the inserted measure, another new measure has been inserted and so on.
With the attached file ... go to the measure number 17 and insert one measure before. Then you can do more different steps from there. Try to change time signature. Or try to delete the (duplicated) time measure. Or try to insert one more measure before the original number 17 ...