It's the whacky implementation to animations that were introduced earlier this year. ZOS wanted abilities animations to be seen versus bash animation being seen. However, if you do it right, all 3 points of damage will go through. Sadly, it is very clunky and a lot of times harder to pull off... It gets even more complicated when you introduce the typical lag of Cyrodiil.
Animation cancelling is more difficult now than it used to be due to said changes with animations.