@mkver
Thanks! That makes sense. In the past I could manually write a BPS tag via an xml file, and back then I simply wrote file_size_in_bits / duration_in_sec as BPS value -- which is also the bitrate reported by oggenc (the ogg container overhead being included, like you said). As such, the definition of BPS value is now incompatible with that of my old MKV files, and I was a bit confused when I noticed that I can no longer explicitly write a BPS tag via xml. Still, if this is by design, I'm fine with that. A 1 kbp/s difference is not a big deal, and most players/tools probably don't read BPS tags anyway
Edit 2019-09-30
In the specs
https://matroska.org/technical/specs...ex.html#BitsPS it is clearly stated that BPS is only the data in the Blocks, and excludes headers and any container overhead.
EDIT2 2019-11-25
If needed, however, you can write a BPS tag freely as you like, by using --disable-track-statistics-tags
For example, you might want to make its value 85000 or 85272.4 or whatever, instead of 85272.