I've had the same issue since (I believe) iOS 7 was released on Sep 18, 2013. I'm also still running iOS 6. The App Store badge will show a certain number of apps (in my case, 5) need to be updated. Then upon entering the App Store, the apps needing to be updated will show the correct number (4 in my case). The cycle then continues/repeats. It may be on Apple's end or it may be some glitch with those devices that are still running iOS 6. This happened before with the iOS 6 release (I believe) and it fixed itself, seemingly over time.