Minecraft 15w32b, Minecraft 15w32c
Java: 1.8.0_25 64bit
What I expected to happen was...:
You can rename your world save.
What actually happened was...:
Instead, I couldn't rename the world.
EDIT: Because you have to hit "Cancel" to save the changes and "Save World" to discard them.
Steps to Reproduce:
Open Minecraft in the new snapshot 15w32b.