You MIGHT want to try a different USB cable.
I'm using my Nook Color adapter(1A) and a generic USB cord which works fine, however one time I accidentally used my Optimus V cable and it would NOT charge while the MT was up and running, however it WOULD charge IF I powered down the MT...
I haven't even tried the cable that came with MT yet... nor have I tried charging via a USB port on my nb, but I imagine that would be REALLY sssslllloooowwwww....
Current Tablets: Samsung Galaxy Tab 7.0 Plus
Current Phone: Nexus 4 (16GB T-Mobile)