[Interest] Arduino TeensyLC USB serial CDC + Qt not working on Windows

[Jason H]

The Teensy provides a virtual serial port via the USB Serial CDC. It works great on OSX.

I have a program where I wrote some code in Qt on my Mac.  My co-worker is trying to run it on Windows 10.
We expected to have to change the serial port name, which we did, to COM4. Teensyduino IDE sees serial traffic from it on Windows.
However, the program writes data to the teensy and expects it to reply back. The program reports having written the data but no reply is received. The Teensy is hooked to a contact switch and it's supposed to send a status message when this happens. He can see characters in the teensy serial terminal. But when we do it with Qt listening on the serial port, no readyRead call back is called.

Does anyone have any idea?
It works perfectly on OSX.