runtime: SerialPort Flush[Async] makes Read[Async] timeout/block

A call to SerialPort.BaseStream.Flush[Async] seems to mess up the state in the serial port base stream so a read following the flush will timeout/block. Write will send data out on the port without a call to Flush, but other classes wrapping streams in .Net Core, like PipeWriter.Create, will always flush, making this issue a blocker. Code below will work if the call to flush is removed. I used a USB-RS232 adapter on a RaspPi3 with pin 2-3 connected (loopback). I have verified data on oscilloscope with and without flush.

@krwq you seem to have worked a lot on the SerialPort for Linux, is this a known issue with Flush breaking the stream?

using System;
using System.Buffers;
using System.IO.Ports;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SerialFlushTest
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var portName = args.Any() ? args[0] : SerialPort.GetPortNames().Last();
            var port = new SerialPort(portName, 115_200);
            Console.WriteLine("Using port: " + port.PortName);
            port.Open();

            var msg = Encoding.ASCII.GetBytes("reader.is_alive()\n");
            await port.BaseStream.WriteAsync(msg);
            Console.WriteLine("< " + Encoding.ASCII.GetString(msg));

            await port.BaseStream.FlushAsync();// Uncomment this line to make read work
            Console.WriteLine("Flushed " + msg.Length);

            using var buf = MemoryPool<byte>.Shared.Rent(1024);
            var read = await port.BaseStream.ReadAsync(buf.Memory);
            Console.WriteLine("> " + Encoding.ASCII.GetString(buf.Memory.Span.Slice(0, read)));
        }
    }
}

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <RuntimeIdentifier>linux-arm</RuntimeIdentifier>
    <SelfContained>false</SelfContained>
  </PropertyGroup>

  <PropertyGroup>
    <SshDeployHost>192.168.1.118</SshDeployHost>
    <SshDeployClean />
    <SshDeployTargetPath>/home/pi/serialflush</SshDeployTargetPath>
    <SshDeployUsername>pi</SshDeployUsername>
    <SshDeployPassword>raspberry</SshDeployPassword>
    <RunPostBuildEvent>OnBuildSuccess</RunPostBuildEvent>
  </PropertyGroup>

  <Target Condition="$(BuildingInsideSshDeploy) ==''" Name="PostBuild" AfterTargets="PostBuildEvent">
    <Exec Command="cd $(ProjectDir)" />
    <Exec Command="dotnet-sshdeploy push" />
  </Target>

  <ItemGroup>
    <PackageReference Include="System.IO.Ports" Version="4.7.0" />
  </ItemGroup>

</Project>