when openning a COM-Port, despite of "none" flow control in the COM-Port settings the RTS line is activated nevertheless.
My suggestion is either to disable any modem control line changes completely if the flow control set to "none" or some additional option in the COM-Port settings what state of the modem control lines to be set upon openning the COM-Port.
P.S. Seen in the source code, file commlib.c, lines 188-189:
dcb.fDtrControl = DTR_CONTROL_ENABLE;
dcb.fRtsControl = RTS_CONTROL_ENABLE;
I mean, it must be _DISABLE per default (a passive state of the signals) or set from some check boxes in a settings window.