Video of it happening:

https://jengamon.neocities.org/altitude_click.html <- EDIT: Video link that actually should work (EDIT now with video embedded on page)

Input that triggered it (in Bitwig 5b3):

Ok, found it in the patch notes:

• The voices control on the top bar now flashes when a voice is stolen.

But if I'm in mono legato, why is it stealing voices for adjacent notes?