Actually I have made a mistake. It's the grenade charge that let's you grapple not a melee. So your question is still valid. My bad. I've not played much with Prismatic, so maybe it's a bug, or it's supposed to be like that. You never needed a melee charge to use grapple prior to TFS, however if you're using it like a banner of war titan grapple melee, then you would only punch if your melee was not charged, where as a charged one will be just like a shoulder charge on a titan grapple melee, if ya know what I mean.