I write the ensemble tag using MP3Tag. I use these to capture orchestras, bands, etc. just as you note. For instance, while I might have the Miles Davis Quintet as a track artist, I will actually set the ENSEMBLE to Miles Davis Quintet (1st) or Miles Davis Quintet (2nd) for either of his great quintets (as just one example).
This actually came out of past issues with other software that would use the ID3v2 tag, TPE2 "BAND" tag (sorry if I rembered the code wrong, I'm quickly going off my memory), as the Album Artist. The don't think that was the intent of the "BAND" tag, but that is what became default, so I had to find another means to capture that especially as I started moving to FLAC files. I think that is when I found the ENSEMBLE tag as something recognized in FLAC and that could be used as a custom tag in ID3v2.
So, I was using ENSEMBLE to specifically avoid the type of issue I am having because the ID3v2 BAND tag had already been misappropriated for that purpose.
I guess it sounds like what I am looking for is more of a feature request since it isn't necessarily a bug, but I do find it as unexpected behavior because I've never seen any other software treat ENSEMBLE that way.
The closest I've seen is that a couple of programs through settings allow one to establish multiple tags to represent Track Artist or Album Artist in their libraries but by default stick with the most basic ARTIST and ALBUMARTIST tags. In other words, if I wanted to include ENSEMBLE, I could define it in the settings.
Given all the flexibility in MusicBee, I find this little nuance strangely inflexible, and it does break my ability to shift to it permanently as I try to eliminate MediaMonkey from my use.