I tried e.g with a CP210x USB TTL Adapter. The device manager in Windows shows it for a second, then disappears, then again. So it is more or less blinking ;-) Guess it is a Parallels USB thing, or am I wrong? Thanks
OK. Seems to run if the device is bound to the VM in the settings and if it is connected to the Mac before you start the windows... If this helps to reproduce something