App Store shows Updates available but can't update

My iPhone shows 7 available updates. When I click the app store and go the Updates button; there are 7 apps under the Available Updates header, but they don;t have UPDATE button only the OPEN button. I do notice that the UPDATE button flashes briefly and then changed to the OPEN button. Of course, by clicking on the OPEN button just takes it to the existing version of the app. And the number of available updates remains at 7.