When running Community Server in a farmed configuration there are some CS Jobs that should not be run on both instances. For example, the Indexing jobs should not be run on both instances because the job will make modifications to the DB and there could be collisions on that job.
Kevin Harder released a list of jobs that should be kept in both instances. All other jobs should be isolated to one machine. Pick your favorite server and make his the "job server".
In a stock CS 2.1 install, the jobs that need to run on every node in the farm are:
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AnonymousUsers
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Referrals
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Views
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ReportingVisitors
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ReportingPageViews
All of the others should only run on a single server.