ispconfig3 imap thunderbird and new mail folders

[Doug G]

I recently set up ispconfig3 on centos 5.3 to try it out, using the perfect server howto. After setting up an email account, I tried to create a new mail folder using thunderbird, but I can only make a new mail folder as a subfolder under the inbox.

From the same computer, same thunderbird, using imap to an ispconfig2 imap account (dovecot) I can create new folders without being under the inbox.

Is this some difference with courier imap, or some configuration issue I missed? tia.