IMCE file browser doesn't list the files in the Directory path that are uploaded by FTP
found it!
Instead of using Filefield_source module I should use the IMCE for FileField module, that's all. Details from project page:

IMCE for FileField allows users to select files from IMCE File Browser. It supports FTP uploaded files by automatically registering them as IMCE files thus making them usable in a FileField.
How to use

Go to your FileField settings page.
Check the box saying Allow users to select files from IMCE File Browser for this field