I doubt it’s a bug; I’m sure what’s happening is you’ve created project-specific custom fields with the same name in both projects.
It’s important to realize that Asana has two types of custom fields: organization-wide fields that live in your custom fields library, and project-specific fields. If you want to be using the same fields with the same names in multiple projects, like with Priority, URL, Search Volume, etc., then you want to add those fields to your custom fields library from one project, then in all other projects, delete the project-specific fields with the same names and instead select the desired fields from the library.