Unable to Change Teams

Not sure if it's a bug but I'm unable to switch teams via command blocks in the recent snapshot. Instead it spits out an error:

"Could not add 1 player to team zombies: Aerotactics"

There's no reason given.

UPDATE: After changing 5 levers to Redstone Blocks and since starting to play 15w34d, everything appeared to work again. It may have been a coding issue, and it may have been an issue similar to https://bugs.mojang.com/browse/MC-51340 but as of now, everything works as planned.