That's looking suspiciously like a sticky shutter curtain. If that's what it is, it could be because the camera hasn't been used in a while and if that's the case it *might* self-correct with continued use. That's a lot of "if's" though. Still, I would try taking a LOT of photos (put it on Continuous, High and just blast away), delete all the photos and repeat this process a time or three. If the stickiness continues over the long haul, you're most likely looking at a professional-level repair.
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