Maildir: do message files need to have a unique name across all directories?

[Gerben Wierda]

While testing a new mail server I created a temporary account and filled its mailbox (Milder, dovecot) with the contents of another account. That means the actual message files in each account have identical names. Is that a problem? (I’m asking because I see some weird behaviour of visible/invisible messages and I wonder if this could have been the reason).

G