I am considering this a bug until told this is expected behaviour.
When a task is converted to a project, any values of a reference field do not carry over onto the resulting within a portfolio with the same reference field. I’m assuming this is an omission in the code.
I have tested this three times in two different environments with different reference fields - same result.
@Forum-team , could you please escalate as this is part of a business-critical workflow we are currently building for one of our customers? Thanks!