Do not add '$db' in reference when referencing document from same $db

When using ReferenceOne or ReferenceMany , doctrine will create fully-qualified reference to the object (with all fields: '$id', '$ref', '$db') even when reference is within same $db.

This approach causes several problems: for example we use mongo database as a template for new clients - when new client registers, template database is copied for him. But since it contains hardcoded $db - copy operation becomes resource consuming, since we have to loop through every document of every collection and fix $db reference.

Also maintenance suffers, since you can't easily rename database when required.

Is it possible to omit $db part when referencing document from same db?