Do not delete instruments ( staves ) separately.
Не удаляются инструменты (нотоносцы) по-отдельности из много-инструментального произведения, невозможно выделить одну партию необходимую для работы. При удалении одно или нескольких нотоносцев удаляется вся партитура.
GIT commit: 3c7a69d
Comments
Google translate (my Russian is too rusty ;-)):
Do not delete instruments ( staves ) separately from the multi- instrumental works , it is impossible to single out one part needed to work. When you remove one or more staves removed entire score .
Still doesn't make enough sense to me, unfortunatly. I do suspect though that this isn't abpout a bug (and pretty surely not a critical one) but more of a suppoer reqtest that should better be asked in the Forums?
There are Russian forums, see https://musescore.org/ru/forum.
The issue tracker though is to be kept in English, so that all the developers understand what the issue is about.
Closed due to lack of information and inability to reproduce. Please report, in English, and with precise steps to reproduce, in a new thread if this still troubles you in the latest version (3.4.2).