Solo on Mixbuses not working [MBv4 on Fedora 24]

[Lexridge]

I have two tracks of MIDI drums going to Mixbus 1 and three tracks of synths going to Mixbus 2. They will mute, but Solo does nothing EDIT: (Solo actually silences everything). Any ideas why this is? BTW, they DO work normally with audio tracks, they just do not appear to work with MIDI tracks.

I am assuming this is something really simple that I am just overlooking, hopefully anyway.

[Lexridge]

Strangely enough, today it is working. I had even restarted MBv4 with no change, then rebooted and the problem persisted. However, today it is working. Very odd indeed! I guess something had its panties in a knot and came out in the wash.