very strange bug noticed, things adding themselves to the cart!!

I noticed if I changed a setting in the Admin, then come back to the front store page, a specific free item I have listed will add itself to the cart. lol It is not easily reproducible, but has occurred at least 4 or 5 times, and always after I change a seemingly random setting.  Just wanted to let you know.  If I leave admin alone and just browse the store, it doesn't happen. And it's always the same product that does it....