Yes, we have noticed something similar.
If an email is sent to a email alias, but not the email address listed in osTicket settings, a ticket is created in the default department, not the department associated with the mailbox that is being collected from.
It is possible to detect this by looking at the email recipients or email headers of the ticket's first thread entry which has the contents of the email.
It is possible to fix this by adding the alias to the OsTicket settings, without specifying any email server or settings, and then the alias can be used with the correct department and even if you like you can choose different help topics etc which is actually quite useful.
Additionally, if the email address is BCC'ed, then a ticket will be created in the default department instead, however you won't be able to see what email it was sent to, so there is no way to fix these BCC emails from going anywhere other than the default department.
