[imp] IMP 3.4.2 ALPHA does not store mails in sent-mail

[Matts]

I have the idea that there is a bug in IMP 3.4.2 ALPHA with storing Sent
mails into the sent-mail folder.

I get the message that sent-mail is not a valid mailbox.

I use a same config on an older Horde config with IMP and there I see not
problems at all, working fine there.

The settings for the user are also the same and setup right.

Can someone confirm this ?