To sum this up, if you are melee charged by an enemy, your weapon is disabled and you cannot shoot for about two seconds. The weapon gets lowered similar to standing in a restricted area. This is the bug that Frenzy players have been getting annoyed at.
I want to reiterate on this; the bug has nothing to do with the enemy just getting too close to your character; in that case, you won't be able to hit them with your firearm, but you can still shoot your firearm. This melee charge bug disables your ability to fire entirely.