Yes... this is normal, but don't talk about it, it's a secret
You have to switch off the REV2 after it has warmed up for about half an hour, wait full 10 sec. and then turn it on again... then do your calibration... then it will go thru the calibration routine without any problems... point is; many users have trouble with the calibration freezing if the REV2 has warmed up first... sometimes it's slow as f***, other times it simply freeze... why it works when switching off and on again i cannot tell you, but I bet it's a hardware flaw...
And don't worry... you can safely turn it off even if it has frozen... you just have to do the calibration again...