If you are on Windows 8:
I had the same issue. The solution is, after a clean install, to connect the printer while windows is running and let it install the driver properly (don't download anything, already in Windows 8).
If you have the printer connected and boot into Windows 8 you don't get the "flatbed" source as an option.
Tested this on Win8 32 and Win8.1 32 & 64 bits.