Lion Mail Reply-to strangeness

I've seen this bug reported a lot in Mountain Lion, but not so much in Lion. I'm seeing it in Lion.

Lion 10.7.5, Mail.app v5.3.

I have an iCloud account and several other POP accounts set up in Mail. I am NOT routing the POP mail through the iCloud account. For simplicity, let's say I have:

a@mac.com (iCloud account)

b@pop.com (POP account)

The POP account uses its own SMTP server, and has been told to "use only that smtp server" in the Mail prefs.

So, if a mail is sent to both a@mac.com and b@pop.com, I would expect the reply to come FROM either a or b, depending on whose mailbox it was read from. If I'm looking at a's mailbox and hit reply, then the reply should come from a. If I'm looking at b's mailbox and hit reply, the reply should come from b, right?

(And my settings in Mail.app say so -- in the Composing preference, new messages are set to come from the "Account of the selected mailbox".)

But that's not what happens.

If the mail is sent To: a, b, then no matter what mailbox reads it, the reply comes from a.

If the mail is sent To: b, a, then no matter what mailbox reads it, the reply comes from b.

(I think there's also weirdness if there's just a cc: of a or b involved, haven't fully characterized it).

Of course if the reply-er is paying attention they can set the reply properly, but really, who pays that much attention?

So, any thoughts? Anyone else seeing this? Any workarounds?