Project 1999 - Can aggro... bug out?!

On my wizard... on a Hate raid... doing my thang...

Timing my nukes based on the speed of the melee DPS. Typically it was start casting Sunstrike at 70%, it will land when the mob is 40% then I maybe I can sneak in a Ice Spear of Solist right after Sunstrike (breaking GCD) for the 1-2 knockout.

It was going great... worked all night... didn't pull aggro once.

Then all of a sudden, I would nuke when the mob was 40% and I'd pull aggro... perhaps a fluke? Next mob... aggro... next mob... aggro. Argh! What is going on?! We pull Maestro. I wait over a minute (DPS was slacking big time) till Maestro is 50% health. I cast my Sunstrike and follow it up right away with a Concussion. I stand still for 2-3 seconds after the Concussion and suddenly Maestro leaves the MT and comes after me (I am full HP), then killing me. People be like... hey why you pull aggro noob! Argh!

I am at a loss... I feel like something went buggy with the aggro. Is that possible? No matter how long I waited to cast a nuke, I was pulling off the MT (whom was a 60 war with epic/vp offhand and was getting tons of procs / white damage). Confused... perplexed. Everything I understood about aggro... gone.