Edit: Found the issue. The client was doing "if action.isTriggered, send triggered, else if action.isHeld, send held". Problem is, when you pressed a key, on the very first frame, it counted as both triggered and held. Client side, it was receiving both on the same tick, but the server had to wait an extra tick before getting the isHeld message.
Edited by Telanor, 10 December 2012 - 10:46 PM.