Civilians on Counterfeit do not react to the pool blowing up

[Meidi]

Had this funny situation just now. Stealthed Counterfeit with a friend while only having Mitchell cuffed, other civilians were unalerted outside. We got to the part where you have to open the doors of the basement, which had C4 on the walls. We didn't manage to defuse them in time and the pool blew up, but civilians didn't react to the explosion at all. Neither did the cop that wandered around the place.
Stealth continued for like 1 more minute and then cops were automatically alerted.