Thanks for fast reply again LeonidM.
Yes, I mean the sample application project which is called in the new project wizard TCP/Serial transfer service, I guess we are talking about the same.
I'm familiar with PuTTY so I've been using that as telnet client. I compared to old TeraTerm installation in Vista machine and opening the telnet session with that didn't result those characteristics.
So, I looked more closely to PuTTY telnet session settings and found out there is selection for telnet negotiation mode. Selecting passive instead of active (default), opening telnet session in passive negotiation mode doesn't send those characters in to serial interface.
Also, opening the session in raw connection type in PuTTY, doesn't send characters to serial interface.
So we can conclude its client and its settings dependent.