Hmm, I'm starting to wonder if my problem is not as unique as I thought. I normally don't try to use the Torch while it is charging, so I could have the same problem as you. However, what I have noticed (thanks to my PC speakers being on) is that when I use the Torch Charging Dock plugged into my PC I seem to get and lose the Lightning icon.
I've since noticed that I will repeatedly get the prompt for Charge Only, USB Driver or Sync Media. I assume that this means the USB port may not provide enough charge?