This has been happening for a few snapshots: When picking out an area and starting to build, chunks will start disappearing, leaving holes in the world. More chunks are affected the longer one plays.
MC-49920
Chunks disappear or become corrupt in 14w08
Resolved
Duplicate
0
Mahamatan
(Unassigned)
Unconfirmed
Minecraft 14w08a
Retrieved
Attached are screenies of the missing chunks near my tower base... ie, they're in my 'active' area most of the time.