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: Nexus 7(2013)
Current Phone: Nexus 5 (32GB/black T-Mobile)