Additional FTP user can't create "lib" folder (permission denied)

hi all,

this is a dedicated server with plesk 12.0.8 and CentOS 6.6

i created a domain, created a subdomain and finally created an additional ftp user with root the subdomain's root folder

i login via ftp client as the additional user and trying to upload the project files. everything is uploaded just fine except of the folder called "lib". ...
can't upload one, can't create one.
i can do everything of the above with the default ftp user but not with the additional one...

i changed to...

Additional FTP user can't create "lib" folder (permission denied)