Quicken does not allow you to suspend sorceries at instant speed. I have tested this both with uncastable spells (like Profane Tutor) and normal suspend spells. With normal suspend sorceries, you're able to cast but not suspend.
The bug is very easy to replicate: outside of someone's main...
On my opponent's turn, I activated the disguise ability of my Dog Walker, turning it face up. While the Dog Walker's ability did trigger, my Sumala Sentry did not. Neither Sumala Sentry nor Dog Walker got any +1/+1 counters.