[CatonaPC©]

There's obviously some scientific explanation for this related to surface tension of liquids. The amount of surface on a dipstick isn't enough to hold the oil for a period of time and eventually ceases to cling to the dipstick . So when you pull the dipstick out, there's no oil on it. Putting it back in is enough to 're-attach' the oil for a measurement.

I'm assuming you are all wiping the dipstick first before reinserting it for a measurement? This is the correct procedure.