Regression: insert an horizontal frame leads to bad layout on undo
1. Load attached file in 2.1-dev a31f66f.
2. Go to the last page.
3. Make literally any edit—move a note, delete a chord symbol, it doesn't matter what.
Result: not one, but two measures on the third system jump to the next line.
Analysis: almost definitely a side effect of a recent fix for #180286: Pushing a system with an horizontal frame causes layout problem, #180991: Layout jump due to bad cautionaryWidth() calculation, or #109021: Hairpin and other symbols are shifting when relayout occurs.