Exceptions list isn't being respected

I usually have checked the option for clearing cookies and site data every time I close Firefox. However there is an exception list where I add sites I visit often and I prefer to keep its browsing data. This list of exceptions seems to be ignored. The sites I have in the list lose all their browsing data. The only solution I have found so far is not check the option to clear browsing data. I remember this function stopped working correctly right after I decided to wipe all browsing data manually.