Hey, I'm not entirely sure that this problem is added by Misty World (since it doesn't have any visible block ID or presence in the creative menu), but by process of elimination, I think it's from Misty World.

Whenever I ctrl-place a cobblestone block, this block places instead:

It's pretty annoying, since it changes the way you interact with such a common vanilla item. It would be fantastic if this only happened in the Misty World dimension, or if there was a way to turn this feature off in the config.

It is the campfire base.
You can disable it in the mod ingame configs.
Look at the campfire -> stoneAndColors and delete the cobblestone line.