Mine has started freezing like that; but I only get it when I turn it on the first time after charging.
I did recently update the firmware; the unit didn't freeze before that - but whether the freezing is the result of the upgarde, I'm not sure.
It's not a big deal, since the reset gets it going again - as long as it doesn't presage anything more serious.
(P.S. just remember - whatever it is - the warranty won't cover it. 
)