When you toss a frag grenade into a room even if you are clear of the blast by walls you will die if you are the thrower of the grenade, this happens with both Soviet and US.

This occurs in any building, the command buildings at Mil bases, and Main bases especially.

The Grenade Launcher munitions as well, affect the original firer more than the AI or players that it is impacting near.

For example, at Montignac tonight, I hit a player directly with an M203 and they lived through the grenade impacting on them, and then through 2 more than impacted beside them, another player in that same instance lived through 2 203's into the radio tent allowing them to capture the the base.

Just a few minutes ago, when I was on one of the official servers, I fired a 203 around a corner and hit the second tree away from the bridge on the south side facing east just north of the Outpost at Meux, I ducked behind the wall and had stopped leaning and was still killed by the explosion even with a double barrier of concrete due to it having to go through 2 1ft layers of concrete+ the earthen mound used for the base of the bridge.

In both instances these rounds were the standard 40mm explosive rounds rather than the DP rounds.