Spell reflection giving XP penalty, intended?

As many other warriors I'm having big issues with my inventory space, so earlier today I had to grind a bit with 1h + shield just to be able to carry more stuff. While fighting caster mobs, I noticed I was getting way less XP from killing mobs with spell reflection than those that I killed without the use of that ability.

Here is the XP gained from killing a level 66 mob without the use of spell reflection:

http://surl.se/ssc

And here is the XP gained from killing a level 66 mob with the use of spell reflection:

http://surl.se/ssd

As you can see, I gain 111 XP less, i.e. -21% XP, by using this ability. Might not be a huge deal but it effectlively translates into 20% slower grinding, in addition to already slow grinding with 1h + shield.

I can see how this works since if we do less than 100% of the damage to a mob we won't be getting full XP, but I thought this only applied to actual NPCs or PCs doing the damage, not a reflect spell. I don't think we should be penalized for using spell reflection in PvE.

Working as intended?