Are you clicking them individually, or are you selecting all then trying to deselect some? If you select all and deselect it ignores your deselections and just remembers that you wanted all of them selected.
It could be a cookie issue. Our current inventory uses session variables and cookies, so if you have multiple windows open on the inventory it can often cause issues with selecting things (though this usually works the opposite as you described, and selects nothing rather than everything, but it depends on what else you're doing).
Also, you were using IE, which could have been the issue. We generally don't even test on IE (I literally don't even have a copy of Windows to test with) and prioritize fixing issues with it very lowly, so I'd suggest using a modern browser like Chrome or Firefox to interact with SWC.