Have you ever seen wrong order in /var/log/syslog ? I think that it causes only crontab.
Jun 28 22:20:01 alex CRON[2327]: (root) CMD (something > /dev/null)
Jun 28 22:21:01 alex CRON[2700]: (root) CMD (something > /dev/null)
Jun 21 03:49:01 alex CRON[2753]: (root) CMD (something > /dev/null)
Jun 28 22:23:01 alex CRON[2754]: (root) CMD (something > /dev/null)
Jun 27 05:08:01 alex CRON[2813]: (root) CMD (something > /dev/null)
Jun 26 00:19:01 alex CRON[2816]: (root) CMD (something > /dev/null)
Jun 28 22:25:01 alex CRON[2816]: (munin) CMD (if [ -x /usr/bin/munin-cron ]; then /usr/bin/munin-cron; fi)
Jun 28 22:25:01 alex CRON[2821]: (root) CMD (something > /dev/null)
Jun 28 22:27:01 alex CRON[3225]: (root) CMD (something > /dev/null)
Jun 28 22:28:01 alex CRON[3240]: (root) CMD (something > /dev/null)
Jun 28 22:30:01 alex CRON[3290]: (root) CMD (something > /dev/null)
Jun 26 12:03:01 alex CRON[3291]: message repeated 2 times: [ (root) CMD (something > /dev/null)]
Jun 28 22:30:01 alex CRON[3291]: (munin) CMD (if [ -x /usr/bin/munin-cron ]; then /usr/bin/munin-cron; fi)
Jun 28 22:31:01 alex CRON[3659]: (root) CMD (something > /dev/null)
Jun 28 22:32:01 alex CRON[3754]: (root) CMD (something > /dev/null)
Jun 16 06:41:01 alex CRON[3846]: (root) CMD (something > /dev/null)
Jun 28 22:35:58 alex cron[909]: (CRON) INFO (pidfile fd = 3)
Jun 28 22:35:58 alex cron[944]: (CRON) STARTUP (fork ok)
Jun 28 22:35:58 alex cron[944]: (CRON) INFO (Running @reboot jobs)
Jun 28 22:36:01 alex CRON[1428]: (root) CMD (something > /dev/null)
Jun 28 22:37:01 alex CRON[3050]: (root) CMD (something > /dev/null)
Jun 28 22:38:01 alex CRON[3082]: (root) CMD (something > /dev/null)
Jun 28 22:39:01 alex CRON[3114]: (root) CMD (something > /dev/null)
As you can see, there is bad time order between lines. It is just crontab error, or there is some problem with system clock, or something?
I am running the latest Ubuntu 14.04 kernel:
Linux alex 3.13.0-30-generic #54-Ubuntu SMP Mon Jun 9 22:45:01 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux