The situation is normal. What you did not see on the literature is regarding the communication between the turbidity sensor and the electronic control. During the pre-wash, the sensor tests the water to see how dirty the load actually is. If there is not much soil seen thru the optic sensor, the control will detract from the wash cycle.
You are not going crazy
If the dishes are getting clean, you have no need to worry. Remember not to pre-rinse your dishes in the sink first, just scrape away solids and load 'er up. Too much pre rinsing causes detergent residue to stay behind and cause other issues later.
If you download the 24" electronic dishwasher manual, it explains the turbidity sensor thusly,
"The true name of the sensor is called the Turbidity
Sensor. It is located just in front of the wash impeller on
the sump. The sensor is mounted by two cross point
head mounting screws.There is a locating tab on the
sensor and a knotch on the sump to ensure the sensor
is intalled correctly. The sensor is a device that senses
how dirty the water is. This is done when the customer
loads the dishwasher with dirty dishes, then starts the
unit. The sensor will then sense how dirty the water is.
The DC output voltage of the sensor will be monitored
at the end of the 30 second pause in the first wash and
the first rinse. If a sufficient quantity of soil exists, the
control will add two additional rinses for a total of eight
fills, or 9.6 gallons of water. Should the sensor detect a
light soil condition, the control will subtract two rinses for
a total of four fills, or 4.8 gallons of water. The Normal
cycle can either increase or decrease the time of a wash
cycle. It just depends on how dirty the water is."