That's correct, Reply To does not affect the From header.
When you have a Reply To, the message should still show as originating from the same address, but if you press Reply on the receiving side, the reply should be addressed to the reply to address.
( sort of like: "Hi, this is Brenda, we're vacationing in the Caribbean, so if you decide to reply to this postcard, send it to Hotel Del Mar, address below, not to my Milwaukee home address..." )
To send emails From a different address, set them up as aliases using Gmail web mail (so it accepts those messages) and configure an additional identity in my app (long press the account / Identities, please see the FAQ for further info.
