Last Access information wrong after restore

Dear All,

I have backup a course from my Moodle 2.1 version, and restore it to another Moodle 2.3 version.  Both are running on Red Hat Linux, 6.2.

The restore done without any error message. But, when I check in the participant list, I notice most of the user 'last access' has already set to 'Never'.  In the Moodle 2.1, the last access of the users have some value. 

I checked the backup file by extracting the .mbz file, and check the user.xml. The last access and last login information are there. Is this a bug with Moodle 2.3 ? Appreciate for the help. 

Please help.

Thanks,

Yulstar