NzbDrone/NzbDrone — comment on commit f56bf629919b4517f226f4b3c1e43ad4735078f6
File: NzbDrone.Core/Jobs/JobProvider.cs line 98
By kayone:

This will cause an issue, every time the app is started the timers LastExecution will reset to DateTime.Now, which means thing like update that run weekly will only run if nzbdrone isn't restarted for a week.

proper way to do it to reverse this logic, get existing job first, then replace parts of it with the new one, rather than create a new one and replace it's ID.