Convert to bill - error msg

Draft recurring bill for director salary, goes into drafts so amount can be confirmed.

The director as the entity is the same entity linked to the DLA.

Click on the bill, edit, enter amount, click convert to bill.

So far so good...

Standard error msg appears saying i'm trying to post a bill against an entity that is effectively a DLA - no problem, happy to continue.

However, the option to convert to a bill now disappears, only leaving update which then re-saves it as a draft.