First person diagonal movement problems

When the player moves Diagonally it starts out not too bad but every time you change your diagonal direction it slows down more and more. until after 3-4 direction changes you essentially have no movement outside of your initial direction.

So if you're moving forward and change between left and right after the first 2 changes you are walking directly forward with a slight list in whatever direction you're trying to go diagonally in.

Is this a known issue with the FPC? Is there a fix for it?