DRanck
I don't see it as a bug. Freezing means bouncing, and you don't / can't bounce muted tracks.
Tracks weren't muted though. The "toggle" on the mute has to occur in the Synth Rack.
Essentially I had full active synths going to fully active MIDI tracks and audio outputs (totally audible and rippin' away).
When I went to the synth rack two of the five synths' Freeze Buttons were grey'd out (unable to Freeze).
By clicking one of the Mute buttons on one of the two synths affected (clicking on the Mute buttons in the actual synth rack) made the Freeze buttons become automagically available. It was weird and I don't think without Songroom's coincidental discovery I would have figured it out.
Probably requires further testing...
I actually now am realizing maybe I created a circumstance that led to this though.... and perhaps I lied a little when I said nothing was muted. The SI Bass track MAY have been muted BUT the new DimPro track was definitely not muted. They were somewhat connected in the sense I manually copied the MIDI clip into the new DimPro track (I wanted the SI Bass track to play through DP instead... and I MANUALLY set up the DP track... I did not let the insert synth options do it for me).
Whatever... if it is a specific bug related to that somehow then maybe I have uncovered something completely obscure (due to manually setting up the MIDI and Instrument tracks then copying the MIDI from a (possibly) muted track into it). The new, unmuted, DimPro track should not have been affected even if the SI Bass track was muted AND by toggling the DimPro instance' mute button in the rack should not have made the Freeze button available on the muted SI track under the conditions you describe.
I am not making any sense at this point so I'll stop but yeah... this may have happened under some strange conditions and may be what happened to Songroom as well.
Anyway... I'll keep an eye on it and see if I encounter any more weird behavior. I am doing a lot of manual synth set up and pasting MIDI into that setup's MID track so if that IS the case this will likely happen again.
Cheers!