Sebilis casters casting through walls
 

That really says it all, you can't LOS their DD spells, or their dots... or their slows, or anything. They continue to land around corners.

2 wiz and a shm pull can get rough~

Better paci up

This was changed for all casting mobs a few weeks ago. You can no longer interrupt a mob's casting by breaking LoS. You have to run out of range.

And this is on purpose? Because LOS was always available in classic...

Quite the opposite. Classic the mobs were able to complete casting even if you weren't in LoS as long as you were in LoS when the mob started casting.

I very keenly remember that walls broke LOS and they could not complete casting in classic kunark AND velious. They could still cast through the ground, which was a little weird, but walls no.

You'll need more proof than your keen memory to get it changed, sadly. Memories have been proved wrong many a time.