Backup and restore

I continue to have some strange problems when restoring old courses. In the proces of restoring one particular course, I got the following message:

Restoring quiz without user attempts. Restoring of user attempts will be implemented in Moodle 1.5.1

What is strange is that both the Moodle installations from where the courses come from and where the courses are restored to are version 1.5.3.

Josep M.