For a wile I try to resolve this together with the RackSpace.com support team but we came to the conclusion it must be a bug.
In the Scheduled Cron Jobs if I edit and job and save it (it does not matter if I really edit or just open and save) then it creates a duplicate entry instead of replacing the job. If I then delete the duplicate it deleted the duplicate but in addition the job above it in the list as well.
This i happens on my RHEL 6 - 64bit server only.
I could make a flash screen recording if this would assist.