The problem is that Reply-To: is overloaded. In one meaning it means
'where you should send messages to reach the person in the From:
header'; in another meaning it's been hijacked to be 'where replies
should go by default'. The two meanings don't cooperate very well;
particularly, there are mail packages which are fairly insistent on
using the Reply-To address instead of the From address (an obvious
lose if you really *do* want to send mail to the author of a message
on such a mailing list).