new update to thunder bird reply field does not auto fill with adress of who you are replying to.
Your latests update does not auto fill the to field on a reply message with who you are replying to from a fresh instance of the program and if you then add an address to the To field and send the mail the next reply message you create for a different person you are replying to has the same address as the first mail you added to the To field.
Wšykne wótegrona (1)
I use Thunderbird regularly on two different computers (one Windows 7, one Linux) and I haven't seen the behaviour you describe.
Can you run Thunderbird in Safe Mode to see if an add-on is doing this?
Try Help|Restart with add-ons disabled, and say yes to "continue in safe mode".