Form Submission emails being duplicated across multiple 5.6 sites... we get 3 of every submission

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Is this a known bug? Within the past few months on multiple sites, we have noticed that when a form is submitted, we are getting (3) identical emails. It seems a cache clear fixes it temporarily, but I was wondering if there was a root cause that anyone was aware of. All websites with this issue are hosted with Bluehost using PHP 5.4.

barkingtuna