Strings with the literal values "true" and "false" are mistaken with bytes when written and parsed from SNBT.

[Igrium]

If you have a string tag with the value "true" or "false" and you write it to SNBT, it's read as a byte when parsed again. This is problematic when trying to manipulate gamerules using SNBT.
Potential fix is to check if a string matches "true" or "false" when writing to SNBT and surround it with quotes if it does.

[DalekCraft2]

Bumping this, because I also experience this. At the moment, I have to use a custom static method to convert bytes into strings, but it would be safer if the issue was fixed at the source.