Chunks suddenly getting higher

Hi, I'm running the latest Bukkit (which isn't helping much, I know - but I'm running the version I JUST cloned off github and compiled; this commit; unless I'm mistaken, this is equal to build #69 from here)

I'm just wondering if others have gotten this error: Suddenly some of my chunks seem like they've been stretched up - tunnels through mountains are suddenly filled with stone, and the mountain above is abruptly higher.

I'd get a screenshot, but it's difficult to tell apart from regular mountains - so I'm wondering if this is only happening to me (I have backups, so it's no prob at all)
--- merged: Jan 17, 2011 7:03 PM ---
Some more investigation has revealed chunks reverting to "just generated" state; also some exception about the chunk loader on the console; I'm running in screen, and have no clue how to scroll up to actually see the whole stack trace
--- merged: Jan 17, 2011 7:04 PM ---

Code:

java.lang.ClassCastException: net.minecraft.server.NBTTagByte cannot be cast to net.minecraft.server.NBTTagShort
        at net.minecraft.server.NBTTagCompound.c(SourceFile:87)
        at net.minecraft.server.EntityItem.b(EntityItem.java:180)
        at net.minecraft.server.Entity.e(Entity.java:749)
        at net.minecraft.server.EntityList.a(EntityList.java:60)
        at net.minecraft.server.ChunkLoader.a(SourceFile:168)
        at net.minecraft.server.ChunkLoader.a(SourceFile:57)
        at net.minecraft.server.ChunkProviderServer.e(ChunkProviderServer.java:122)
        at net.minecraft.server.ChunkProviderServer.d(ChunkProviderServer.java:57)
        at net.minecraft.server.PlayerInstance.<init>(SourceFile:32)

--- merged: Jan 17, 2011 7:31 PM ---
Addendum; as posted by these users: http://forums.bukkit.org/threads/chunks-beig-replaced.901/ and http://forums.bukkit.org/threads/craftbukkit-build-69-not-saving-world.883/ it seems the chunks regenerate, and poorly.

If I'm going to make an educated guess, the server fails to load the chunk due to the NBTTagByte cast problem, gives up, then regenerates either a default chunk or some horrendous abomination of nature.