Installed our Moen faucet this weekend. Temporarily screwed in the faucet to test it out.

It's a single handle (Posi-Temp) Moen Monticello.
Feed: 3/4 Copper out of the water heater to 3/4 PEX. 3/4 Pex splits to 1/2 inch Pex going to the tub and 1/2 inch Pex to the sink.

It seems like the flow out of the tub faucet isn't right. If it's on anything but full hot or barely on at all, the flow seems to not stay tight together but instead flatten out and separate.

Video here: http://www.youtube.com/watch?v=bRLLCVlk0N8

Is this normal, or is it usually a tighter, more column-like flow? If it's not normal, why? What can I do about it?