Where are you seeing the 8.28/8.3V? On the scruteneers voltmeter? The cells will drop off as soon as they are charged. Are the cells showing 8.4V on your charger display when it terminates?
If you don't balance charge do you get the same result? Have you tried measuring the cell voltage with a voltmeter during charging and compared the reading with that on the charger? It may be that the charger is reading too high and terminating the charge early.
Sorry for all of the questions, just trying to see where the problem may lie
