I'm having the same problem as well. As for the part of it replying using the wrong account, it is discussed (though not solved) at https://discussions.apple.com/thread/4143652?answerId=19050717022#19050717022
Just to clarify, if I have the email address of me@a.com and me@b.com, and I get an email from you@b.com which is sent to me@b.com, and has someone@b.com in the cc, if I hit "Reply All", the reply email is set up to go to you@b.com with someone@b.com and me@b.com in the cc. This is *WITHOUT* having the option to include myself in the cc set. To make it worse, since me@a.com is my default account, this reply (even though it was sent to me@b.com) comes from me@a.com.
If I were to just hit "Reply" - and not "Reply All", the reply email will go to you@b.com, but will be from me@a.com (again, the default account) - however, I am no longer included in the cc (because, again, I *don't* have the option to include myself in the cc set).
It makes it pretty hard to manage emails...it used to "just work" - but not anymore. Every time I reply, I need to remember to check the "from" field - and every time I reply all, I need to remember to remove myself from the list.
BTW - This is the same behavior as the iOS Mail app as well - and has been since the very beginning.