I have the external footswitch and the MidiMaestro connected.
I am using the Midi Maestro to change the BPM.
While the BB main display shows the recently changed BPM value in huge font, the unit will not respond to the external footswitch - in my case it is mapped to stop the song, and as such, it will not stop.
The same happens if I change the tempo from the unit itself with the third dial.