Behind the scenes, the mod subscribes to the on_tick event and keeps adjusting the walking speed while the avatar is moving. I can imagine that this doesn't play well with latency hiding in multiplayer, where your client shows you where it thinks it will be until it gets an update by the server with the real position, and the server in turn probably has a different idea about it all because it receives input events later.
Unless I have a brilliant idea or there's something new in the factorio API I haven't seen yet, I don't think I can fix that.