It's just the history of your updates. The OPEN button is purely a convenience in case you want to open up the updated app to see what's new. New updates will show up at the top of the list with an UPDATE button, or a circle/progress icon if still in the process of updating.
There is no way to manually clear the list, but it cleans itself up automatically; removing the oldest updates from the list at about the two week mark.
If you are set up for automatic updates then other than searching your home screens for blue dots the update list is about the only way of figuring out what's been changed lately. This is the most likely reason for the list's change in behavior. It also preserves the update descriptions in case you want to look them over.