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It's possible that you were facing enemies that can reflect projectiles, for example chakrams, impale, rapid fire, ect.

Here's a few monsters that can do it:

http://diablo.wikia.com/wiki/Dune_Dervish

when they spin they can reflect physical projectiles back at team mates and kill them

http://diablo.wikia.com/wiki/Sand_Dweller

they have a sand shield attack that on hit can reflect projectiles back at you