grubbin shouldn't be a problem but hitboxes for large pokemon like drampa, turtonator, and larger legendaries are to the top left of the sprites. its not exactly a bug, that's just where the hitbox is.
i haven't checked for other browsers/devices but for me the item icons that replace the cursor aren't exactly centred either.
aim high and left for large poke, low and right for small poke. i guess i've just been here long enough that i'm used to it :/