Elsie, sorry I'm a little ~ vague at times
Waste: Don't understand "limp on with a patch for a season or two if there is a leak that doesn't get found until you open the pool."
What I meant was that if there is a small leak degrading the bottom, and subsequently causing undo liner stress, any damage done between now and May, when you open the pool and can fully check it out - can probably be fixed for a year+ with a patch before having to replace the liner.

So water CAN evaporate even with a tight lid? Ok, I'll monitor and check in with you down the road. Stuff stops falling from newly budding trees (of which I have hundreds) first week in May and then I uncover.
There was a thread about solid covers allowing evaporation http://www.poolforum.com/pf2/showthread.php?t=527 - I was less than credulious on that (but could be wrong !)

From your 'follow-up' post I strongly! suspect that you have a small hole in your solid cover and that you are pumping out pool water when you 'automaticly' pump off the cover. This would also explain the debris that you see at the seams of your pool - the cover water and the pool water are mixing - and what happens to one is happening to the other. This is the basis for my earlier ?#1. I hope that this is all it is and that you do not have a leak in your liner!!