Freemarker inspections are inconsistent: some built-ins are marked as type-mismatch errors

Most often, I get errors that say "Type Mismatch: Built-in _______ is not applicable to 'String'". I've had the blank be 'substring', 'number', 'index_of', 'replace' and others. See image.

I'm unsure why this only happens about half the time. Regardless, it's annoying and it'd be appreciated if you would fix it. 

You can see the error indicator multiple times in the following code, and the info popup on one of them.

Thanks!