Deck lifting?

Hello everyone,
I have done a few partial drains and refills to lower the CYA levels in my pool. The most I've drained is about 12 inches, but I've noticed that one corner of my pool, the deck has lifted up nearly an inch from the tile that it usually lays against. The deck portion is about 4 ft long, and the lifting is only affecting the one end. The affected area is an "outside" corner - it juts into the water. It is almost like the decking has sunk downward a bit on the side away from the water, making the decking at the pool edge lift a bit.
The first time I noticed it was after the first drain and refill. I just did a third 8 inch drain and the gap seems to have increased by a quarter inch or so.
My pool is about 8 ft from a hill sloping down from it, and the house has more upward hillside across the street, so I assume that the water table can't be too high - wouldn't it flow down past my property which is on a flat zone of the hill?
Does anyone know if this is likely to be from the partial draining? I can't be sure this is new - I may have missed it when we purchased the house 7 months ago. We've had a couple hot weeks, so the ground may be drying out a bit.

Thanks,
-Carter