These aren't really clear answers to these questions:

http://eo.yifan.net/users/j/melkor/read_receipt.png

Does clicking "Cancel" cancel the whole message or is it "no" ?

http://eo.yifan.net/users/j/melkor/logout_sure.png

Ok, the latter is clearer than the first one, but still not very good. Better for both would be "yes" and "no" options. Or is this JavaScript limited?

From my experience, the Cancel for message receipt means "No".
Have not tried the other one, why would I?

I assume this a standard JS script with a variable question-text (or just lazy/lousy programming).