Duplex scanning does not work

[doktrova]

Summary of the issue

The duplex setting on the enum for the double-side document has a value of 4. I believe that value should be 5. 5 throws an error. However, even when corrected to 5 it still does not scan both sides. From previous experience, for duplex, the transfer function of the should be called twice. I don't see that happening in code. Let me know if I am missing something or this is really a bug.

Thank you,

Don