Nostalrius Begins - Quality wow vanilla realm (1.12)

Quick question,

Has anyone noticed improved drain soul not working as stated. Yes I have searched the boards, but there are conflicting statements. It says it has a 100% chance to proc, but mine doesn't come in at nearly that - closer to 50% of the time. Yes I pull off pet to get last killing blow. And I have even tried without pet out and still does not proc all the time.
This is a big issue with the class if it is not working.

Drain soul must deal the final hit on the mob for improved drain soul to proc. At least that's how I remember it from vanilla. They didn't fix/change it so that it just needs to die under the affects of drain soul for the buff until TBC.

You must deal the final hit on the mob to kill it. Whether it be drain soul, or any of your curses, it will proc. However, if your pet does the final damage to hit, it won't proc unfortunately, what I usually do when I cast drain soul is I put my pet on follow.