After properly saving and exiting from Minecraft through the menu buttons, then reloading the world, changes made to certain chunks would be erased, and returned to their seed condition.
The furthest affected chunk I have been able to locate was 7 chunks away from where I was standing when I saved and quit.
All placed/removed blocks in an affected chunk are reverted.
The lost materials are not returned to my character's inventory.
Only chunks altered for the first time during the current session seem to be at risk.
Chunks that have previously been modified in some way and successfully saved do not seem to be affected.
The chunk where my character is currently standing always seems to be affected.