Because the clock doesn't pass through the times 2:00-2:59
on the first day of daylight savings time, jobs (such as my
daily backups!) that are scheduled to begin anytime in this
one hour window are skipped.
Arguably this is correct in the sense that these times don't
exist, but if this behavior is to be considerd "normal",
then the man page should warn users about this.
Your suggestion has been passed on to a developer for further review.
I have reviewed the Single Unix Specification definition of crontab
(it doesn't talk about cron specifically, but the crontab definition
talks about the crontab format as well) and there is no indication
that cron should magically re-schedule jobs that are scheduled for a
non-existant time. Indeed, it is not clear what the right thing to
do would be if cron tried to shuffle the schedules.
I have reclassified this bug report as a documentation bug report
and we'll change the man page to explicitly mention that cron will
not run jobs during times that do not exist, such as during daylight
savings time conversions.
Man page updated with this information in vixie-cron-3.0.1-32
Following up on this, in RedHat 7.3, the cron manpage makes no mention of
daylight saving time. It is not clear whether some jobs may be run twice or not