Adding multi-stave instruments causes problem with brackets joining those multi-staves.
How to generate the problem
Open a score, Reunion is fine.
Add a keyboard instrument, piano or harpsichord.
The existing brackets at the left of each line should remain in place, the new instrument should have its own brackets.
The new instrument has correct brackets. The existing bracket is extended to cover all four staves.
Could there be a priority between "normal" and "critical"? This isn't critical, but it is important.