While i am playing i save and quit the game and get when i get back only a portion of what i did before i saved it saved.

Example:
While playing minecraft i made a shaft mine where i was digging in one direction. i mine a good 30 blocks then i made a trap door and placed where i needed. the shaft where i saved was roughly at point X:78 Y:14 Z: 51. so then i saved and quit the game came back 10 minutes later and i was at point X:79 Y:63 Z:33. and also when i came back the newly dug out shaft and the trapdoor were both gone. This happens just about every time i save and quit.