Dishwasher Detergent Dispenser Not Opening Properly?

Our Maytag dishwasher detergent dispenser has a wax motor to open the dispenser door. Recently, but not after every wash, when opening the dishwasher at end of the wash and dry cycle we found the liquid soap had dripped down the inside door and become hardened and dishes and silverware are not fully cleaned.

This seems to indicate that the dispenser opens, but at the wrong time late in the cycle after the wash and rinse and possibly opens due to the heat in the dry cycle. If the detergent door didn't open at all I would be sure it was the wax motor, but since it is intermittent, sometimes functioning correctly, we are baffled.

We made sure the spring is clean and functions (the door snaps open), the hinges are clean and not gunked up, and gasket is sealing well, the door catch funtions. We opened the interior door panel and removed the wax motor checking its electrical connections for oxidation (they were clean) and made sure the plastic parts to be moved by the motor to open the door moved freely. There was no detergent residue in the motor area or assembly.

What do you think is happening? And what can we do about it?