I can confirm that the mouse x mouse y and mousexy (2dAxis) only work during key button presses at my end too. Infact LMB down returns movement LMB up stops it. RMB click or click and hold makes all movement show until i LMB click.
Seems this is linked to the mouse buttons and not a continuous stream as would be expected from say a thumb stick.
guessing my on tick method is looking good right now no? 
strange behaviour