This condition in incorrect. If you have two circuits tapped into one breaker 15 or 20 amp by a wire nut or any other means and there are twenty outlets on total from both lines than this one circuit is overloaded and not safe. It should be corrected. If a circuit line is shortened in the panel and a wire nut is used to extend it to the breaker that is allowed. As to nuisance tripping, that potentially is a safety concern since you really can"t identify the cause with out further diagnosing the problem.