Well... it's not normal, but what's going on is probably easy to explain.
Normally, if you are running VA and you unplug your microphone, VA will generally detect it. Instead of just giving up, it hangs around and waits to see if you plug your headset back in or if you've changed to another device. In your case, your mic is put to sleep by Windows and then VA no longer sees it. Windows is probably presenting another device as your default device and VA is picking it up (which is why VA is not responding... its using another device for input). I'm not sure what you can do other than you can try adding a hotkeyed command that has a switch audio device action in it. Other -> Windows -> Change Audio Devices and select your microphone from the list. Let us all know if that helps!