Low level mobs don't miss anyore?

Last week, I was running some low level dungeons on my 80 to plvl someone. Was going through ZF repeatedly for fast levels. Got it down to where I could go through the whole instance in 4 pulls minimum, or 5 comfortably. I did 10+ runs pretty much the exact same way.

This week, I log on with the same character, same gear, same buffs, same everything. I try to do the first pull, exactly the way I did it last week. I almost die. I get further in, and I realize that things are kicking my butt. I did some testing, and it's no small difference, like 10%, or 50%, or even 100%. I'm having to pull about half as much and losing about 4-5 times as much hp. That's a difference of 800%+.

Talked to my brother, and he had noticed the same thing when going through stocks. Before, the mobs would miss almost without fail. Every now and then they'd land a hit. This is how it's supposed to be, as they're level 20. This is how it worked in retail when I played back in WotLK. Now, they hit like trucks and hit about as often as they previously would miss.

What the heck broke in a matter of just a few days?

Edit: Just thought I'd add that I originally noticed this on Lordaeron, but then my brother was playing on Icecrown when he noticed. So it seems to be a cross-realm sort of breakage.