Falling blocks are glitching out.

Please attach the crash report ([minecraft|http://hopper.minecraft.net/help/finding-minecraft-data-folder]/crash-reports/crash-<DATE>-client.txt), otherwise we can not diagnose this issue.
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I also had gravel on a flat ground that I can't pick up.  I mined out the blocks under them, they fell and jumped back up again.  I filled in the blocks I'd mined out from under them, and they went back to sitting on the ground, but would not go into my inventory.  When I read that you logged out and back in again, I tried that and they immediately picked up into my inventory.