Drain life(all drains?) stops when you stop facing target

[Lelol]

What is the bug?
Drain life(possibly all drain spells) stops when you stop facing target
What kind of bug is it? (Quest, Class, Spell, PvE)

How can you reproduce it?
Duel someone, start draining, have him zigzag you very closesly, run around you, run through you etc.. The drain will sometimes stop midcast.

You can also test it by dueling someone and casting a drain spell, then manually turn around so you no longer face the target, the drain spell will then just stop.

Please describe, in detail, what is suppose to occur when this bug happens:
drain spells only require you to face the target when you start casting the spell, after that it only cares about range, and nothing else.

Please describe, in detail, what happens when it bugs up, and how it's malfunctioning:
It just stops the cast. This started happening after the 01/02/15 update.

Evidence providing proof of bug:
Is it really needed? Could try to find some video if you really want me to but this is quite obvious.

[Itslovelol]

Fixed.

(Don't know when live.)