A new bug has been exposed in Battlefield 4 that may be the source of many of your annoying deaths. The “death shield” bug results when a downed opponent, who still could be revived, is between you and your target. If this happens, the hit box from the downed player remains standing and blocks all incoming damage from you even if the animations and explosions play out correctly.
YouTuber jackfrags exposed this game-breaking bug and reported it to the developer but this could definitely be the source of many frustrating failed ambushes. A downed player in front of you acts like a shied taking all damage and causing grenades to bounce back.
Battlefield 4 was released back in October of 2013 and the fact that major, game breaking bugs are still coming to light from users is telling of just what shape this game was in at launch.