Hi!
I finally got this working! And I may have an explanation why it didn't work at first...
To make it short, I had to reinstall LDAP after I had created my test users and shares. I used the command "/usr/share/ebox-usersandgroups/ebox-usersandgroups-reinstall", but - I can't remember precisely - the accounts were not really deleted OR they were deleted but not the users' homes... So finally I had UID & GID confusions and mismatches.
After I have deleted all the accounts, groups and shares manually and reset them, the logon script worked as expected.