What may cause duplicate nodes to be created using a Rules action to Create New Entity?
According to the current status of issue # 2783453 (which IMO should be a support request), this looks like something else is happening in your site.

Something that will help you find the answer to your question, is to have a look at Rules debugging ... Within the Rules settings, experiment a bit with the debugging facilities that come with Rules. At least have a look at the "Rules Evaluation Log" (to check that the Rules logic being executed, actually matches what you expect that logic to be).

For way more details about Rules debugging, refer to the answer to "How can I display the value of a variable inside a condition?".