Because of cURL, I think you need to use AddHandler, instead of just AddType. AddType changes the MIME type of the document, and the server should process the document according to that new MIME type. Because the MIME type does change, this is not the issue. The issue is that the server doesn't know what to do with a document of type application/x-httpd-php, so it simply serves the document to the client. AddHandler creates a specific link between the file extension and the script handler. I would still recommend trying the following:

AddHandler php5-script .html

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