The only conundrum I've had and that I can't explain with Mojo is that it gets significantly hotter when playing from my MacbookPro than from my phone. I can play and charge from my phone at the same time and it doesn't get anywhere close to as hot as it gets from my laptop while playing and charging. My first mojo had a defective battery, I would only get ~10 minutes on blue, 1.5 hours on green, the total play time was something like 2 hours. Drew @ Moon audio took care of me and got me a replacement.
The secret of using Mojo playing and charging at the same time is keeping its battery full.
I had heating problems when used Mojo charging and playing at the same time but not having a full charge. (Shut offs.)
Since I keep Mojo fully charged, I have no problem with charging and playing simultaneously.