I would like to explain this change.

I know a lot of people really love OSM and do whatever they think is the best for project and data that it contains, but in this particular case the existance of this "border" does not really mean anything in real world.

Russia claimed for a lot bigger territory at the beginning, including 70% of Kharkiv region, a lot of Mykolaiv region and so on (check https://deepstatemap.live/ if you are interested in the location where there vere the battles). Less then a month till "referendum", russia stated that they wouldn't ever leave Balaklia and Izum

De-facto (you love those words, ha?), there is no border where this line was added, the whole territory is recognized worldwide (with little exceptions, sure) as part of Ukraine.

Spend you energy in better ways, e,g. improving address database or adding new buildings.

Have a nice day.