Beyond how it happened, that is a good safety reminder for us all.Seals on the valve core can seep air as Bill notes and they may do it at lower pressures, so reset the tire to the correct pressure and watch it for a couple of days.If it turns out fine -- making vandalism more likely -- then I would blame it on Waylon,Willie & the boys, you know they're always up for a feud.Take care and enjoy the ride,Greg