Input won't stay as a dropdown when I save the project

In this project:

The block should look like this
firstclass-colors script pic (5)
but instead looks like this
firstclass-colors script pic (6)
whenever I load it. The options and read-only are checked, and updating them seems to fix it (un/rechecking). This may be related to Newlines are replaced by spaces, as they both happen when loading the project and can be temporarily fixed by updating the value

Just to add, this doesn't happen in every project.

Aha, I found out the problem! This only happens when you have a block with a lone percent sign and a dropdown menu in it. Then it would be more similar to this bug.

Thanks for tracking this down. The use of in-band signalling (text characters with special meanings) in blockspecs is imho one of the unfortunate things we inherited from Scratch.