I'm not sure if this is who this issue belongs to but I've noticed that Return Receipts aren't working properly if you turn on the "Return Receipt" preferences.
If I select "Always Remove Return Receipts" in the preferences:
AND showing the "Additional Mail Options" check boxes, I cannot select the Return receipt checkbox.
If I try to set them via the Delivery Options dialog, it will accept the check on save but still not return the receipt. Also, I noticed on the test I ran that the ReturnReceipt field will be set to "0".
I tried reversing the preferences to "Always Honor RR" and no luck.
Thanks!