OSX Yosemite, Java should be up to date.
I was testing AreaEffectCloud NBT with impulse command blocks. I would summon an AreaEffectCloud with custom NBT.
1. For my testing, I only changed the NBT radius, radius per tick, particle, and effect.
2. I went into survival to test out the effect.
3. I summoned the potion,
4. walked into the cloud (Wither lvl 6),
6. switched back to creative,
and I could no longer edit command blocks.
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here