As I said in my original post, it only happens when the message I'm replying to has my address in the "to field plus one or more others. When I receive the copy of the message I just sent in my inbox my email address appears again in the "to" field. This doesn't happen with the standard android email client or gmail or any other android, windows client or webmail that I have ever used.
ps, Of course I used google translate to read the reply that was posted in russian before posting here and while it made sense it didn't actually give an answer to the problem.