This is really annoying when you are escaping someone or something or just trying to run somewhere
You can press space whilst running to avoid this. The reason the person stops (correct me if I'm wrong mods) is to nerf the running-faster-with-your-hands-up thingy. When sprinting at "ready" you're charging, and to avoid abuse you've got to stop to interact. I dunno why it happens when you walk normally though.
@Oysterz yeah, but if you don't press space while there are 5 zeds after you, you will end up dead because you stopped. I almost died today because I stopped when I took the Fire axe into my hands.
this is especially annoying because you need to be in the raises stance for melee to work.