Venue 10 Charging

Out of the box it appeared that the battery charged at a low rate when the system was in use and the charger was plugged in. My Venue 10 is now 8 months old and the battery slowly discharges when the system is in use and the charger is plugged in. In the diagnostic mode (F12 when booting) the discharge rate without the charger is 1768 ma and with the charger plugged in the discharge rate is 257 ma. 

This appeared to be a fault in the tablet so I sent it in for "repair"  All they did was to replace the charger USB cable which, of course, is not the "problem". 

Slowly discharging the battery during system operation while the charger is plugged in isn't a major problem but doesn't seem to be a good design. The charger is rated at 10 watts and there is a warning in the documentation not to use a more powerful charger which is interesting.

Has anyone else seen this "problem"?