Loads of interesting theories and good advice here. As a player of [eek] 40 years I am philosophical about this now. I have had this problem on and off for years - more so with Stratocaster type guitars strung through the back but with acoustics too. Keep plenty of spares and buy a string winder thingy is my advice. It's a bit like punctured tyres - nothing for ages then 3 or 4 at once. Pencil lead in the saddle and nut is a wise move, though. Or you could take up the melodeon...