The same thing wouldhappen if you took it off the charger immediately when it goes green the first time. The Incredible's problem is that as soon as the lightgoes green it goes back to battery power, whether it's still plugged in or not. The drop you see that first ten minutes is the battery indicator catching up to how much power has been used since it turned green.
So, you're doing the same thing as a bump charge. Forcing it to restart the charging process to reclaim those few percentage points it has used since reaching full charge.