Inserting / appending horizontal then vertical frame causes system to split
Use the attached MuseScore file:
Insert a horizontal frame before bar 1. Now insert a vertical frame or vertical text frame at the same bar. The brace and staff name break away. If there is no name, then only the brace breaks away. This happens with more complex systems also.
Now go to the final bar. Append a horizontal frame, then append a vertical frame or vertical text frame. The brace, staff name and a section of the bar line breaks away from the end.