IPad is charging, but the battery is still going down?

I've noticed some odd charging things since I updated my iPad 2 to iOS 7.1.1.
It was 25% charged a while ago, so I put it on the charger. But every time I look back at it, the battery is still going down!
The little bar at the top right of the screen has the little charging sign next to it, so there shouldn't be a problem that the charger isn't properly connected.

Anyone know what's wrong?

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