PLEASE REOPEN IT IS NOT A DUPE ISSUE AS ITS BEEN MARKED SEE MY COMMENTS AND EVIDENCE IN COMMENTS BELOW.

It is possible that a player can be reported as standing on 1 or 9 separate locations. This will at first sound crazy, but if I player is stood on the edge of a block due to internal rounding or flooring of the X and Z co-ordinate.

There is NO way at all to know what block the player is stood on. This has huge consequences to the game. The simplist way to duplicate this is to stand on the edge of a block and run the following.

/setblock ~ ~-1 ~ minecraft:stone You should expect this to replace the block the player is stood on but if you are on the edge of the block there is a good chance it will change the block in front of to the left or right of the player.

Please see the attachments. Note that every shot the player cords have not changed. Note this can happen any side OR corner hence why the player can be internally seen to be standing on any 1 or 9 blocks.

mc using the center of the player's aabb, even though you can still stand on a block with less than half your aabb is likely the cause.

I have tested this also in 1.7.10 and 1.7.9 with the same results. It occurs in Survival or Creative mode and in single of MP. The same result.

Hope you understand that, please treat this as a matter of urgency as this has huge effects to so many areas of the game.

Regards
Relicum
PS I am Dyslexic so sorry about any spelling or grammar.