Abilities fail near the exit

[(XBOX)KayAitch]

This took me by surprise and I think it might be a bug.

I have a Riven to beat a high level exterminate mission undetected with an extinguished dragon key. So Ivara + Madurai + constant Prowl + Covert Lethality.

I beat most of the mission got to the exit and found 5 enemies standing at the exit, just enough to finish. So I snuck up to them and all of a sudden my Prowl cloak dropped and failed me the Riven challenge.

Just to be sure I tested it and about halfway up the steps my ability turns off, regardless of my energy or anything else.

Is this a bug or is it deliberate? If the latter then enemies shouldn't be able to enter the exit area.

[GnarlsDarkley]

Usually only extraction turns off your abilities. e.g. I can stand invisible/in the Rift in extraction w/o problem until the marker turns green. I tend to run to the exit (= look for it) in Mdef with Limbo and chill my base in the Rift on extraction without leaving the Rift

Edited October 11, 2018 by GnarlsDarkley

[(XBOX)KayAitch]

So is it just Ivara's Prowl? 

[Guinylen]

Any ability is disabled when you're at the extraction before the mission objectives are completed.