Your last photo looks like you have it pretty full. At this water lever, a loss of several inches a day should produce a wet spot down hill somewhere...unless it hits a long underground vein of gravel/permeable earth. Underground water travel can be very tricky.
I would guess you have one of two scenarios (or maybe a combination of the two). 1.) Your pond bowl is made up of permeable soils and the water just weeps out everywhere. 2.) You have a vein at the bottom taking the water away.
I have read of folks performing the "bucket test" to determine if the clay is worthy of using in the bottom of a pond. Do a Google search for "Pondboss bucket clay test" and you'll get some reading on the subject.
