Playing on a Vanilla 1.9 Server I host. The blaze are able to throw fireballs through the walls. Not sure if actually through the blocks, or they are getting between the blocks placed diagonally of eachother. There is no space for any fireballs to get through. I was hit while walking through the hallway and you can see the fireballs coming through. These are all spawner-generated blazes. The Blazes had already aggro'd before the walls were built. When logging off and back on they lost aggro. After re-aggroing, the problem persists.

I was unable to catch a picture of the fireballs coming through the hallway as they moved too fast. There is a screenshot of me getting hit by one, as well as a representation of how the hallway is built.

P.S. May be related to "Blazes seeing player through walls"