I'm betting that it will work the other way around too if both are BBS##-B motors. Put a 36V BBS##-B controller on a 48V BBS##-B motor and run a 36V battery (and change the volt setting in the display).
The reason I asked is I now have two batteries, one 48V for both of my Bafang rides and one 36V for one MY1018 ride. If I buy a 36V controller for one of my 48V Bafangs and use the 36V battery, then I can take both Bafangs out with a friend if I want to.
If anyone has successfully tried this please chime in. Or if you don't think it will work, please let me know. Hate to spend for a 36V "B" controller and find out it doesn't work after the fact. Thanks.