Yeah, that's a glitch. The A.I. is running into a logic error. The factions can't decide to shoot at the enemy behind them or you. The vision of the A.I. knows you're there, but also knows they can't hit you because of the glass.
I have played F.E.A.R. since release. I've played through it several times.I've seen an enemy vault over a short wall, push over a crate to make cover, throw a grenade, then rush me. I've seen an entire team of enemies camp a chokepoint and open fire as soon as I came into view. Some will even retreat, find an alternate path, and attempt to flank you while you're dealing with the rest of their team in the front. The game's A.I. is outstanding.
What's sad is that a game that was released in 2005 still holds up to this day with regard to its A.I. I think the only A.I. that has come close has been Crysis 3, and Crysis's A.I. is smart, but not dynamic like F.E.A.R.'s.
As far as terrible experience from a game as soon as I bought it, the worst experience in the past 5 years has been Diablo 3, hands down. Got a refund after I hit 60 and realized it was total garbage. Man, was I mad.
"I refuse to prove that I exist" says God. "For proof denies faith, and without faith I am nothing..."
-Levelling up games. "You couldnt hold a knife before, NOW YOU CAN!!!" -Games that have "magic hands (Bioshock, etc) -Anything with Buffs, perks, CARE PACKAGES (UGH!!) and all of that nonsense -MMORPGAVROFLS...yeah, anything which is defined by letters.