I opened a ticket about this (reported it as a bug) already, but I figured I would add a post here in hopes that someone else noticed what triggers the effect...
I have noticed that at times, my own character and others start to run like their armor is chafing, or I became very bow-legged... my speed is not really affected and if I stop and start to run again I run normally.
As I am now aware and noticing this, I have seen others whose armor is also chafing.
Of all the things I have lost, I miss my mind the most...