>> That option was and is off, but the recipient of my messages informed me that he started getting my messages with the "read-confirnation" requests.
Hmm.
When you have a chance:
Do you see "Read receipt requested" on Aqua's compose window, before sending?
Are your messages replies or new ones?
If they're replies and *his* messages have "read receipt" -- THAT'S IT, found it.
When replying to a message with "read receipt" request, the reply will have it too. Wrong, that's a bug, will fix.