Flash FormData upload to S3 generates duplicate filename param and bombs out upload

[KnownSubset]

Trying to have Flash send mOxie.FormData a mOxie.File up to S3 causes a duplicate input field to be written out for the filename.

403 error response received from AWS.

<Error>
  <Code>AccessDenied</Code>
  <Message>Invalid according to Policy: Extra input fields: filename</Message>
  <RequestId>A109BA6CF4DCA803</RequestId>
  <HostId>wJbsevGMqL6yzG7QlSWKpBXNbXE25Ep5UnmZKuRhCRP9udjw/Lz2pR2aZb+KXafAXvhRfktDsaA=</HostId>
</Error>

Request payload:

------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="Filename"

fonts.pdf
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="key"

development_bucket/fonts.pdf
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="x-amz-server-side-encryption"

AES256
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="policy"

eyJleH....
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="x-amz-credential"

AKIAJQGS5W3QIWU46C3Q/20161006/us-east-1/s3/aws4_request
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="x-amz-algorithm"

AWS4-HMAC-SHA256
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="x-amz-date"

20161006T213545Z
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="x-amz-signature"

b4187....
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="file"; filename="fonts.pdf"
Content-Type: application/octet-stream


------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7
Content-Disposition: form-data; name="Upload"

Submit Query
------------Ef1ei4Ij5KM7GI3gL6cH2Ij5Ij5KM7--

I believe it has to do with Flash auto-inserting the Filename input field and the filename being included with blob.