Sieve: fileinto :create issue with Public Folder

[dovecot at avv.solutions]

Hello Community,

I face the following issue:
- using a sieve script to file into a existing private folder: ok
- using a sieve script to file into new private folder using ":create": ok
- using a sieve script to file into a existing public folder: ok
- using a sieve script to file into new public folder using ":create": NOK !

The returned message is: "Permission denied" and the message correctly 
falls back to inbox.

HOWEVER, if I run "doveadm mailbox create -u myuser at mydomain 
Public/TheNewFolder", the folder is created, and the delete command 
works as well.

Any tip?

Running dovecot 2.2.13 on a pi/debian jessie

Thanks