Mail message import question

I recently used MailMate to import some previously exported mailboxes to my account. The mailbox folder hierarchy contained subfolders within subfolders. For example:

Test1 —-|
| Test2 -—| | | | Test3 Test4

Test1 and Test2 contained no messages, Test3 and Test4 did.

I used the File/Import Messages… dialogue and checked “Create IMAP mailboxes for subfolders”. Test1 pre-existed on the server and after the import all the folders and messages were in place. However, when checking in webmail, Test2 could not be subscribed giving a “Mailbox does not exist” error despite appearing in the folder hierarchy list.

Repeating the process with a message in Test2 created the mailbox proper and it could be subscribed.

So my question is should an empty mailbox be created rather than a placeholder in the folder hierarchy?

This came to light as a mail backup program I was testing failed accessing the IMAP account as it could not build a list of the mailbox folders. Recreating these folders fixed the problem, although I have asked the developer to check their app as well.

Thanks.