Overguard is removed regardless of whether or not the Pack Leader is installed.
If anything, on the contrary, it works fine up to 1200 while equipped with Pack Leader. (I don't have Primed, so this is a prediction, but probably 2200 if Primed).
It happened to me and my friend.
I have verified further and it seems to function properly while wearing the Pack Leader. However, once the limit is exceeded, every time you hit a melee attack, it will decrease to the overguard limit of the Pack Leader.