PVP scaling depends on attack time, so the attack speed bonus could have a significant effect on how much PVP hits with multistrike are scaled compared to non-multistrike hits, separate from the damage modifier? Might depend on a bunch of other factors how much that affects results. I'll try to do some quick testing.
I can see the numbers in-game right now and it definitely applies correctly. I can breakpoint the bleeding damage roll and see that the values are different on each hit, and look at the stat values applied to the monster by the debuffs, and see they match those rolls. My first hit rolls bleeding in the range (806-1465), resulting in 1125. The second rolls in (984-1788), resulting in 1636. The third rolls in (1161-2110), resulting in 1767. All three bleeding debuffs are then on the target, with those values, and only the last one is affecting the enemy, because it's the strongest.