Why Does Water in Toilet Bowl Drop
Assuming that the water does not continue to drain after it reaches the half-inch drop, I believe that what you're seeing is by design (intentional or otherwise). When the tank on the toilet refills, a small portion of that water goes to the toilet bowl to refill it. The bowl is typically overfilled to ensure the water level fills up to the edge of the siphon (I'm going to refer to it as such, even though this is not the name on many newer toilets) to prevent sewer gas leakage, and the excess drains over the edge. I suspect that your toilet is of such a design that the water level inside the siphon equalizes slower than one would expect.

There are a number of reasons that the water level could equalize more slowly; some models create a back-pressure inside the siphon, some create a positive air pocket for additional suction during the flush, or it could just be the intentional design of the siphon. 

I doubt it is something to worry about.