I found several different threads on this, but the title for this one seemed to apply to me the most.
Currently running on 8.1 beta 2 on my iPhone 6 and 8.0.2 on my iPad rMini. I usually update apps through iTunes to avoid having the same app download multiple times.
I've noticed that since 8.x, after downloading and transferring updated apps via iTunes, the badge doesn't go away (change in behavior since 7.x).
I've noticed that on both the iPhone and iPad, when I go into the App Store app and then the Updates section, these apps will show an "Update" button, which then changes to "Open" after a second or so.
Also sent feedback to Apple.