Not a “bug” per se, and you’re not the first to notice/mention it.
Renoise/Redux represents MIDI note 0 as C in the octave 0.
Live/Bitwig represents MIDI note 0 as C in the octave -2.
Some other hosts represent MIDI note 0 as C in the octave -1.
Yes, it’s a bit confusing, but it’s not a bug.
All notes are functionally identical — ie. MIDI note 0 is still the lowest possible note you can play in the host, and it will still trigger the same thing everywhere — it’s just that each program represents/displays that note 0 differently.
Please refer to the following thread for more info:
https://forum.renoise.com/t/octave-mismatch-between-ableton-and-redux/43507