Maybe I'm mistaken, but it seems that every-time I commented out a crontab entry,
it will deleted automatically.
ssh server crontab -e // commented out an entry using "#" // save and quit
crontab -e // notice the previously commented entry is disappear
User is root, using vi as editor, running on CentOS 5.7,
and the version of crontab (from man crontab) is Cron V4.1