Alright, I'm not entirely sure if this is a bug or a change from the way spawners work, but I could not get customized spawners to work.

What I expected to happen was to summon a slime spawner with this command:
/setblock ~ ~1 ~ minecraft:mob_spawner 0 replace

What actually happened was I ended up with a pig spawner. I was not in sunlight at all, and gamerule DoMobSpawning was off. the difficulty was Hard. I messed around with the other usual arguments, and giving it a custom name made the name show above the pig but nothing else changed no matter what.

Steps to Reproduce:
1. Paste the command into a command block.
2. Run the command.
3. Watch as you get a pig spawner instead of the expected outcome.