brent Maybe its cookie auto delete?
That's possible. I don't accept any third-party cookies, but I do accept and keep all others. Without those, sites I visit routinely (like my credit union and places where I shop) don't retain certain information about me (even the ones I want to do so), and it makes life difficult. I got tired of constantly re-entering data that should have been remembered from one session to the next, and stopped blocking or deleting all cookies.
The only reason I can think of for third-party cookies, though, is for tracking me from site to site. I can't see any upside for me in that, thus I don't accept them at all.