[Dovecot] Asterisks (*) in Folder Names disallowed?

As far as I can see the RFC for IMAP should allow the * character in the folder name. This is certainly allowed in UW IMAP.

Dovecot seems to object however with:

ERROR : Could not complete request. Query: COPY 9975:9975 "mail/*myfolder" Reason Given: Invalid mailbox name.

Could this restriction be lifted?

Best wishes, Daniel