I've seen this before and I actually made a thread on it to.
I haven't seen the 20x shooting speed glitch tho.
And yes it will NOT shoot if you upgrade the turret THEN an enemy shows up and so your turret will just stare at the enemy.
The turret WILL shoot if it is already shooting a target THEN you choose to upgrade the turret and so the turret will shoot and then get its upgrade.
Hope that helps, they really need to fix that. Seriously, just look at a UNSC Supply Pad when you upgrade it and think about what you see.
I'm a beast in Deathmatch.
Not so beast in Standard but can still kinda hold my own.
Currently looking for decent partners in 2's and 3's whether it be Deathmatch or Standard.