In my application I can open a serial device with hardware flow control or no flow control. I have an RTS checkbox for toggling the status of RTS when there is no flow control and a DTR checkbox for toggling the status of DTR.

In hardware flow control mode everything works as expected, DTR can be toggled.

In no flow control mode disabling DTR also wrongly disables RTS. If DTR is then enabled it does not re-enable RTS, the RTS checkbox has to be unchecked then rechecked to get RTS reasserted. Expected behaviour: toggling DTR should have no impact on the RTS status line.