I had recently playd on a poro king match where i ulted morgana as she shielded and i could not exit the ult and it got stuck on her, i thought if she ults it not only nullifies my ult but i can exit my ult. It would not let me exit my ult i was stuck on her.
You sure she didn't just Bind you and you were trying to cancel by walking away?
did love this but poor 
did not.
Plus you can exit your ult as malz, but it would not let me.
I will abuse this against every malzahar forever
Her shield isn't her ult. Black shield is one of her basic abilities and all it does is prevent CC on the target and block some magic damage. The canceling part is the only bug.
Ya my bad on the ult part, yes you are correct the bug is the part where i was stuck on her and could not cancel. Thank you for fixing my comment it was confusing.
This is the correct behavior. She doesn't interrupt your ult if she shields it. She simply prevents the supression. You can continue to ult her (and deal damage once her shield breaks) and the channel continues.
