I've found that sometimes with mobs that charge (i.e. boars, stags) you'll wind up with the target LOOKING like it's in one place, when it's actually in another. The problem with this is that you have to be in a position to attack it based on both where your computer THINKS it is, and where it actually is. i.e. for you to hit the button, your computer has to think the mob is within range. But for the button to work, the mob has to actually be in range. I think it's part lag issue but also part issue of simply having your pet make an intercept against a charging mob.
I've also noticed some issues with mobs and terrain in the new patch, i.e. beasts bouncing up and down, etc. So it might be patch-terrain-ish-related or it might be the charge-change-aggro issue.