cron.daily run time creep

OS: SuSE 9.3 Pro I found my cron.daily files were running at all sorts of times of day in 9.3 (several systems) and finally found a message posted earlier this year that told how to fix it by removing the /var/spool/cron/lastrun/cron.daily file at the time you wanted it to run - one minute. I set mine to run at 4:00 AM (0800 UTC) and it did so the first day but then ran at 0415 the second day, 0430 the third, etc. What causes this creep? Am I going to have to run a cron.weekly job to reset cron.daily? Thank you, Lucky Leavell