There's an easy solution for that. Next round, hold the grenades for a count of five after arming before you fling them into the room.
LOL! I don't know if I'd hold it for five!
We were always taught to cook it off for 3-
"one one thousand, two one thousand, three one thousand- Grenade!"and toss it in the bunker, fighting position or room. As a matter of fact, I have never been taught any other way to do it (cooking off the grenade for such obstacles) and was a little surprised the SF guy made any kind of a big deal out of it- maybe it was just the reporter who tripped out on this detail. The SF type actually should've done it that way to start with because a cook-off is SOP for that obstacle.