Same issue here.
Happened to me twice on 4.2 and once on 4.4.2.
The first time it happened I was on my first charge. It just died around noon going from 90% to 1%.
I chatted with Motorola the same day and agreed on keeping the phone to see if the problem solves itself when the battery gets a...
You may try and clean the USB-port on the Legend. It does accumulate quite a bit of dust over time and may prevent good contact.
I got a replacement unit after 15 months because of a broken camera and noticed that the usb cable fit much tighter and went in quite a bit deeper than on my old...
I also installed zeubea's CM10 alpha3 latest opus and I love it. It is really fast and responsive and I haven't had a single reboot.
There's some glitchery going on though; touching the trackball spawns a virtual mouse which works just fine, but I prefer using the trackball to highlight menu...
I use to get that unresponsive screen issue only in the summertime, plus it gets worse if I add humidity (read: sweat). I just need to give it some time then to dry off/ cool down outside my pocket, and it's all fine again.