I found this issue when trying to use a TNT cannon I made. Before the 16 update(yes I waited), it worked properly. It relied on the dispensers spawning the TNT inside another dispenser. After the update, the TNT now spawns in a completely different area.

Instead of the dispenser spawning the entity into the block, it will look for an open space making it spawn in an unwanted space. In my testing the direction of the dispenser does not matter, and it functions like a bed.

If it helps this is in experimental edition.
 I have not tested if non-solid blocks behave the same way, but for all other blocks, it behaves this way, so it's not just because it's a tile entity.