I'm slightly suspicious of these numbers :)

I have a powertap hub and use a fluid trainer. I noticed today that every time I stop for a few seconds, and restart, power leaps by about 10w... to the extent that having done it half a dozen times over the course of a workout, my decoupling was -51%.

Is this normal? Does the powertab recalibrate during these stops? My power numbers are essentially meaningless as a result.