It also looks like something similar happens with some USB connections to a PC. See this post: Battery Percentage Indicator
For me, my PC charges the Tour just fine, but I know that not all PC USB connections put out the same power, which is why some externals come with a UBS Y cord so you can connect to 2 USB outputs. I think this is/was especially common on laptops.
Anyway, the question here is: Does the Tour have some special requirements on power sources that make some 5v USB connections iffy? Since my 8830 was fine with a source that my Tour totally fails with, something seems to be different.