i dont know if this is a bug or it is so you can aim right and left properly but here goes :

when you aim directly above or below your player the bullets dont go straight to the middle of the cursor, they go to one side. go try it and see.

I think it may be because the cursor isn't meant to be that precise.

ah but even at very close range with any weapon it still does it

Look at your Soldat and look at the cursor, the weapon muzzle isn't pointing directly at the cursor anyway. Add in the fact that each weapon has a certain accuracy to it and bullets don't always fly "straight" out of the barrel of a gun. You could go even further and say that wind affected your shot.. but that's just me saying that.

i think it is to make the nullets head towards the middle of the cursor at a further left/right distance