Sure. It's common for server or client side scripts to overwrite cookies, or cookie expirations. When you embed something that depends on cookies in a third par

Sure. It's common for server or client side scripts to overwrite cookies, or cookie expirations. When you embed something that depends on cookies in a third party site, you have very little you can do to keep the site owner from nuking it unintentionally. Browsers frequently eat cookies for no good reason. Safari has been the biggest offender in my experience, but I've seen it in several. These are two really common issues I've personally dealt with, I know there are more but I can't think of them off the top of my head. EDIT: No, I'm not aware of any way to detect how/why a cookie has been deleted. It just vanishes.