Dishwasher opening the soap dispenser within minutes of starting

I may be incorrect on this, but have noticed recently.

I put a tablet in the dispenser and close it.
Close the door and start the dishwasher.

As its filling the dishwasher with water and the prewash cycle is beginning, the dispenser door opens.

If the pre wash water is soon pumped out, the disolved soap may be going out with it and the main wash is not getting the full benefit of the wash cycle.

Anyone seen this problem or is that correct behavior?