Verified by several crossbow users when playing DTV and siege: Crossbow bolts do not hit straight in the center of the crosshair, but instead seem to deviate a bit to the right, forcing to compensate by aiming to the left of the target. Something misaligned the aim, somehow.
Edit: It also feels like the bolt deviates upwards, a bit like a thrown weapon, rather than in a straight line and then down.