Can't be down to spec/auras, as they're all Frost/Blood Presence, and all have cut and pasted config files/identical (or working towards for the new 2) talent trees.

Can't be down to gear as it still happens when the characters are naked.

I put a Minor Speed enchant on, and the problem is that bad that even that hasn't completely fixed it.

The only thing I can think of, is I got hit by some kind of movement debuff, and it didn't go away properly, corrupting my character data on the server