[imp] renaming an deleting folders

[ianux]

I have a folder in my INBOX called test.
When I rename it, a pop-up window ask me for a new name, and show the
actual name INBOX.test.
When I rename it to INBOX.test2, IMP create a folder in INBOX called
INBOX, and inside this folder, another one called INBOX too, and inside
it, test2.
When I rename it to test2, IMP create a folder in INBOX called INBOX,
and inside it, test2.
And if I want to delete it, IMP does not allow that, saying
"Mailbox does not exist, or must be subscribed to".
Why this behaviour ?