Crash is triggering open hihat via MIDI

Weird - doesn't do when running via the internal sequencer, just if being triggered by MIDI - can anyone else see if they have a similar thing?

And just as mysteriously, it's not working fine.. I did replace the one of the faulty 74HC165N ICs, which I wouldn't have thought should make a difference, but I've not done anything else and it's now working as it should...