Here's an interesting one which I've just noticed. I have cities with locked units. The tooltip says "yada yada ... but will be unlocked if attacked".
But "attacked" doesn't seem to mean besieged? If the besiegers just sit outside the walls and wait to starve me out, these guys never get unlocked. The problem with that is that they then can't sortie to support an external relief force and that was a shame since they would have added considerable firepower.
Is that all by design?
I had the idea of dragging them out of the city on blue/green, so they'd get attacked and unlocked and fall back into the city. That actually worked but since there was no way to coordinate the move with any external force they lost a fair number of troops and cohesion in the exercise since they battled first. Not ideal.
Is there no way to unlock them just by virtue of being under siege? After all they are being attacked... kinda...