Hitting issue with shotgun/smg

I've noticed some combine being seemingly too damage resistant, mostly in the case of shotgunning them in the face, other full health combine seem to die, while combine of the same type can sometime live through not just one close range double barrel shot, but an additional normal shotgun blast as well.
When this happens, I don´t see blood sprays on them when hitting them, while it´s clearly hitting, I know blood is client side, but since the combine doesn´t seem to be taking damage it seems both client and server disagree on the shotgun hitting.

Check this out at 5:04 until the point I die. The first combine takes a full barrel hit, and two subsequent normal shots(from farther distance but still the first double barrel was in his face)
http://www.youtube.c...aT-88w8#t=5.04m

If you look really closely(may have to rewind a few times) you can see an impact(spark?) happening at the fuel tank thing directly behind the combine, as if the shot passed through him. This was recorded with a ping of 20-40 with no lagg noticable.