See https://community.openhab.org/t/startup-error-for-all-cron-based-rules/14405/25
It seems that CRON based (and System Started) rules do run multiple times (unless you edit them and force them to reload). Some Events from startup below - note both of the startup rules are triggered on system started.
2016-11-22 12:25:02.201 [DEBUG] [untime.internal.RuleRuntimeActivator] - Registered ‘rule’ configuration parser
2016-11-22 12:25:02.211 [INFO ] [el.core.internal.ModelRepositoryImpl] - Loading model 'Bathroom.rules’
2016-11-22 12:25:02.734 [INFO ] [el.core.internal.ModelRepositoryImpl] - Loading model 'Power.rules’
2016-11-22 12:25:02.830 [INFO ] [el.core.internal.ModelRepositoryImpl] - Loading model 'NodeAlarms.rules’
2016-11-22 12:25:03.104 [INFO ] [el.core.internal.ModelRepositoryImpl] - Loading model ‘GeneralSecurity.rules’
2016-11-22 12:25:03.725 [DEBUG] [ntime.internal.engine.RuleEngineImpl] - Started rule engine
2016-11-22 12:25:04.216 [DEBUG] [e.internal.engine.RuleTriggerManager] - Scheduled rule ‘Fan Run Values for Graphing’ with cron expression '0 0/3 * * * ?'
2016-11-22 12:25:04.223 [DEBUG] [e.internal.engine.RuleTriggerManager] - Scheduled rule ‘Check Time’ with cron expression '18 * * * * ?'
2016-11-22 12:25:04.279 [DEBUG] [e.internal.engine.RuleTriggerManager] - Scheduled rule ‘update time’ with cron expression '53 0/17 * * * ?'
2016-11-22 12:25:04.329 [DEBUG] [e.internal.engine.RuleTriggerManager] - Scheduled rule ‘Radio Alarms’ with cron expression '23 * * * * ?'
2016-11-22 12:25:04.371 [DEBUG] [e.internal.engine.RuleTriggerManager] - Scheduled rule ‘CPUUpTime’ with cron expression '13 * * * * ?'
2016-11-22 12:25:04.374 [DEBUG] [e.internal.engine.RuleTriggerManager] - Scheduled rule ‘update time Alarm’ with cron expression ‘7 */19 * * * ?’
2016-11-22 12:25:09.393 [DEBUG] [ntime.internal.engine.RuleEngineImpl] - Executing startup rule ‘StartupBath’
2016-11-22 12:25:16.614 [DEBUG] [ntime.internal.engine.RuleEngineImpl] - Executing startup rule ‘StartupGen’
2016-11-22 12:25:24.703 [DEBUG] [ntime.internal.engine.RuleEngineImpl] - Executing startup rule ‘StartupBath’
2016-11-22 12:25:25.244 [DEBUG] [ntime.internal.engine.RuleEngineImpl] - Executing startup rule ‘StartupGen’