First GetADC using DT_Analog.pbp incorrect measurement afterwards is good. Why?

I am using Darrel Taylor's DT_Analog.pbp for taking analog measurements. Measurements are taken in a loop using GetADC.
The first ADC measurement is always an incorrect value. After the first measurement, all consecutive measurements are correct.
To get around this I do a single measurement first. Then I run my loop to take multiple measurements using GetADC. What is the reason the first measurement is always bad or incorrect?

Your help is always greatly appreciated.

Bryan