System.IO.Ports Flow Control?

I've got a device that uses XON/XOFF Flow control..

I've knocked up some sample code to send data to it... please excuse the hacked together nature of it but it is here: https://github.com/davidwallis3101/SerialGateway/blob/master/SerialGateway/SerialHelper.cs

Im using the latest nuget pre-release in .net core 3 with visual studio 2019 preview 2..

If I run the code on windows 10 - works fine the, the device gets the 'on' and 'off' toggled correctly.

if I then try it on Ubuntu 16.04 - it doesnt work and appears like its ignoring the XON/XOFF values, which the device uses to block comms when it cannot process them, so there is a window when they are permitted..

I'm using the same USB-RS232 adapter between the machines, I've tried different chipsets CH vs PL and no difference..

Is there something that needs doing on the host, outside of dotnet for the this to work on linux, is it supported / tested?