This is now happening on my replacement phone! I got the first phone replaced because it wasn't charging but now it's happening again on the replacement. It seems to only happen when the battery gets to 20% or lower. When it does this, it doesn't matter if it is USB or wall charging. I have been able to get the new phone to charge now twice by rebooting - one time it took three reboots. The first time it happened on my first phone the battery widget stuck on 50% and I didn't get the low battery warning and the battery went to 0 before I knew it and it took forever to begin charging again. I've been on different battery modes when it happens, so that isn't causing it.
I've mentioned this on a couple other threads and there's been others that responded it happened to them, so I thought I'd start a thread on this in case Motorola is monitoring this forum (they better be). Anyone else chime in here so we can get a feel for how widespread this may be.