Bracket Change removes player groups?

Or something. I’ve got a string orchestra piece that includes a lot of (2-part) divisi coming in and out. My preference is to have the standard vln1/vln2 sub-bracket in place at all times, with an additional sub-sub-bracket when either part divides, along with just a single sub-bracket for viola and cello when they divide. (Apparently this functionality has improved in 5.0? I’m using 4.3.)

Just to make sure: Is there any way to make that happen through the various settings?

Not having found one, I’ve been making this happen via bracket changes in Engrave Mode, and for the first 9 pages it’s been great. On page 10 (ms. 57), vln2 splits, and I’ve been trying to add a sub-sub-bracket (in addition to the sub-bracket that includes all violins).

Not only does this not add the sub-sub-bracket, it also removes the existing bracket, along with removing all the barlines between staves for the rest of the piece.

Anyway, file is attached.
AS - Dorico Forum Version.dorico (1.2 MB)