MHL adapter (11 pin) won't fit in S4 (SGH-i337m)

I have an 11-pin MHL adapter (it's the long one which slides deep into the phone) which I used regularly with my old S3. I now own an S4 (SGH-i337M) and the adapter *should* fit and work, but does not do either. The plug won't slide fully into the connector; and sitting loose and halfway in obviously doesn't establish an MHL connection. When I shine a flash light into the port on the phone, it's clearly too shallow to accept the longer 11 pin plug.... which makes no sense as all specs and info on the phone indicate that the S3 and S4 should use the exact same 11-pin adapter. Can anyone explain this; or explain how I can use MHL with my new phone?

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