Disappearing message when move to Inbox subfolder

We are using dovecot 2.0.9 on Centos 6.5 and having the following issues for one single user/single mailbox.

When an Outlook (2016) user creates a folder under their Inbox, it does not create in their mailbox (checking with webmail the folder is not there). If they drag a message to that folder in Outlook, then it disappears. Ive searched their mailbox using doveadm and its simply gone.

Ive tested with webmail doing essentially the same thing and it works with no issues.

Any ideas here would be most well received :)

Thanks in advance,

Simon