This is not a bug, why is this posted here?
Because not everyone knows how the game mechanics work and i'm not even sure what to think of it these days after it has been changed so many times. Not everyone can be all knowing...
Also, those two screenshots are a little misleading... Due to the tree being smaller on the right and side, it makes the crosshair look smaller than the left hand one, if you understand what I am saying. An illusion so to speak... I'm going to draw lines and see what it is like lol.
Edit: After drawing lines, it does appear that the right hand redicle is smaller than the left hand one, however i'm not 100% convinced since I have seen comparisons between normal Crossbows and Masterwork Arbalests with the same wpf and the Arbalest still seems to be a less accurate... But this is about Power Draw increasing/decreasing accuracy, not crossbows!