I have no idea of how to fix it. But i did small tests these days and didnt notice that bug, i just checked it right now and u are right, but its like a "microsec" xD. I will keep using ur model. If u fix it, great, but if u cant... Is not such a great deal, i mean, u need to be staring at the unit to notice it, in the middle of a fight im not sure if u will notice it.
I would recommend u to not get mad with it or waste time working vainly on it. Ask others how to fix it and work on it only when u have an answer or u figured out how to solve it. Meantime dont worry, the model is cool and unique anyways. Maybe is imposible to fix and thats the reason why never there were a crossbowman like this one xD
Greetings