Have you found that your logs are dated in the future?
When a course is backed up and restored with user data, if the start date is updated (say to the day it is restored), all the logs for that course have their time offset by that amount also.
This is a feature rather than a bug as even if you kept the logs at their old time values for the new course, they would still be incorrect, as the logs would appear to exist even before the course began.
If you are backing up a course and restoring to make a new course for a new semester, its best not to keep log data.
If you are restoring a course to a special location for auditing purposes, it's best that you keep their original start date.