HCT test with USB serial driver

Hello,

I'm using HCT 11.2 to test my USB serial driver. The driver basically
simulates a COM port (COM3 in my computer) on the Windows side. I
tested it as universal class.

I couldn't make it pass the Surprise Removal test. The test log
basically says

"I cannot find COM3"

But I suppose since my USB device is surprisingly removed, there's for
sure no COM3 exist any more.

Is my understanding wrong? If yes, how do I correct this problem?

Thanks a lot,

Alex