Spurious line break after removal of line break on previous system

3.0.1, Windows 10

1) new score, treble template
2) add line break to measure 2
3) undo, or select the line break and delete

Result: measure 21 (or whatever was the last measure of the second system after step 2) is now on a system unto itself. It's as if there were a "soft" line break on that measure after step 2 that isn't deleted (although I know there is no such element).

Fixes itself on next "full" relayout.