Save and Quit Problem

Hello, i have been working on a minecraft map, but for some reason, every time i build in this one place in the world, when i log out, and then anytime when i log back in it has been erased! i thought it was because maybe it was a small bug and i started building again and it disappeared! i went into another place in the world it didn't erase it, the only way i can build there is with any minecraft world editer(mcedit, etc,) if you want any videos of this event happening, tell me, please solve this problem.