tis true
An oversight for sure. Many characters can't use their abilities in ult (say bebop) but some others can (like venator and infernus) and sinclair doesnt seem to inherit logic for it and justs blocks you from using your abilities in any stolen ultimate.
OP should post their matchid and timing when this happens but its quite easy to recreate
modifier_citadel_tossup is not being removed from calico if she ults while under its effect. therefore she cannot move
Casting Lil Helpers from some specific angles onto the Sinners Sacrifice will cause Lil Helper's pathing to break, causing them to be stuck, unable to finish their task and thus unable to return. This will be the case until either a player or another helper enters the camp and clears the sinners...
it is relatively easy to reproduce. kelvin has to move towards the target (doesn't matter whether it is friend or enemy) and use the dome. if the target is stationary the bug is more likely to occur. although as of writing this, i can't reproduce it 100% of the time.