BUG - arpeggiator on/off automation doesn't work unless track is selected

This is similar to the ProChannel module on/off automation problem I just posted. 

To reproduce: create an automation lane for arpeggiator on/off on a MIDI track. Create an envelope which turns on the arpeggiator at some point. Start playback. 

On my system, the automation only works if the track is selected. If I select another track, the automation is ignored. 

At the risk of sounding an ass, is this some setting or feature that I'm just too thick to suss?