We are developing two packages: baseline package and package extension. Baseline package has CustomMetadata__mdt custom metadata and package extension contains additional field to this custom metadata.
When 'skipvalidation' parameter is used, it is possible to build and use package extension which contains additional fields on the custom metadata included in the baseline package.
However, when I try to create a validated version to release a package extension version, I receive an error "You can't create custom fields on installed managed custom metadata types.".
Why it fails only when I try to create a validated version and works just fine when I build and install two beta versions of the package?
What are the options to overcome this problem?