Q: Time Clock stops when ipod goes to sleep

My Daughters Ipod Touch 5, whenever the ipod blanks the screen (goes to sleep), the system clock stops.  If its active the clock runs fine.  Tried a software restore to the newest version.  Still no better.   This is a particular inconvienance if she accidently locks her Ipod (or her sister does) because you can only unlock it by keeping it awake for the entire duration.   Otherwise it says "try again in xx minutes" forever.

Any ideas?