In Creative mode, 2 blocks break/place at a time after dropping scaffolding on fire

So I was seeing what would happen if you dropped scaffolding on fire. For some reason, instead of putting out the fire, it broke on top of it. After that, I noticed that whenever I try to break/place any blocks, sometimes it would act normally, and other times it would break/place 2 adjacent blocks.

Mojang, can you help please?
Thanks,
Unspeakable203