At a guess, I'd assume someone swapped out one or both pickups for better ones. I'd want to know if it were mine. (I do want to know, and it's yours! ). If you've never taken a guitar apart before, it's quite easy to have a look underneath the pickup to see if there are any identifying markings. Loosen off the strings, and unscrew the four screws in the corners of the pickup surrounds (not the two height adjustment screws in the middle.) There should be enough wire there to turn the pickup over and have a look at the base. Let us know what it says, or post a pic. And, glad to hear that it tunes OK now. A little trick to help, is to lubricate the nut slots. Graphite is a good lubricant. Scrape the tip of a pencil with a craft knife so the dust goes into the slots. It is the first thing I would do if a guitar ever had any tuning problems.