If you are higher than clouds, and you break a block, with a small render distance (e.g.: 6 chunks), you can see that clouds, that you're not supposed to see ('cause of the render distance).
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[media][media]

Duplicate of MC-9553

Is this still a concern in the current Minecraft version 1.7.9 / Launcher version 1.3.11 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.