From what i recall it is not a bug, it is a positioning issue. This positioning issue may be a bug, but its vanilla like.
We started having issues with the melee on our warlock also, for three straight attempts, then we changed the positioning of our warlock tank to be about 15 yards from vek with the warrior tank in front of him just standing there, and not a single melee since.
TLDR: you can prevent the melee with proper positioning
It appears to be a multi-variable issue. A combination of distance, positioning with respect to the floor design, the stairs (we have found if the warlock is at the top of the stairs it does not trigger melee, only if he is at the bottom on directly on the stairs), and depends on where the warrior is standing.
My warrior on those pulls always directly took the port for me and stood in front of me while I was casting most times. If you watch one of the videos from 2006 that was posted in the other twin emps thread on this forum it clearly states warriors need to always anchor the boss not just on teleport.
Anyways the warlock discord has confirmed this is vanilla like, they are just working out the details on what exactly is happening.
I’m leaning toward range, along with others in range (closer?), and not terrain. In the four kills I’ve been a part of, no warlock was on the stairs.
Just by googling the issue one can find clips where the warlock is at the correct range, on the floor away from the steps, and has had aggro for 6+ seconds taking 2-3 shadowbolts then seemingly randomly Vek’lor stops casting to charge in and start meleeing.
Nothing about the problem was ‘fixed’ by what the warlock did. The only thing that stopped the behavior for a kill was having a warrior stand just out of AE range and between Vek’lor and the warlock tank.
Like everyone is re-iterating, this has nothing to do with stairs. The entire raid can be on the exact same floor as the boss, the snap aggro absorber can be within or outside of AE range, it doesn’t matter. If this didn’t happen to you, you lucked out.