Another bug, I didn't know where else I should report this:
Set the LFO to Free mode
Connect the brute to an external MIDI clock source
The LFO goes freely, as it should, while the arpeggiator syncs to the external clock.
But if you stop the MIDI clock, when the brute latches back to its own internal clock, the LFO switches to Arpeggiator-sync mode.
That's the bug, but a related feature-request: maybe some way to toggle external or internal tempo sync on the device itself. So that when an external clock is stopped, it doesn't switch back to its own tempo, which is most likely different from the external one.