balancing questions

Hi,
I am a new guy to the lipoly field.
I have notice that after the balancing process is done,several minutes later the cells are not held within the same voltage.
The cells have different voltages shown in the charger several minutes later after the balancing charging is done.
I thought the cells are advertised as matched cells ,and these situations should not happed.
How about your lipo cells? Does these happen to you?
My charger is Hyperion Duo and battery is trakpower.