number of websites stored cookies keeps changing
In Safari Preferences, Security tab, there is a summary of the number of websites with stored cookies on my computer. This is normally constant, but now keeps flicking between two numbers, one about 1000, another about 300. When I click on the Details button, the site names displayed also appears to be flicking between two sets of names every second or two. If I click on an address to highlight it, the whole set of names is replaced by the other set before I can click the Remove button, and then the original set comes back, but with the one I originally highlighted no longer highlighted. Does anyone know how I can stabilise this? Tried simply quitting Safari and also re-starting the computer.
MacBook Pro, Mac OS X (10.7.5)