I upgraded from the latest snapshot to Pre-1. I was in the Nether when I loaded my world and I got hit from nowhere. It turns out that the blazes could shoot through the blaze spawner I blocked off.

But I got damage and set on fire through the wall. I have captured a video of it:

https://www.youtube.com/watch?v=yVlBL8oa_Pg

I have to admit that I'm unsure if I got damaged from something or a fireball that went through the wall. I'm also thinking that this might be a problem due to EntityCramming rule (that is set to default in my world). So, I really don't know what is happening here.