Bukkit

What steps will reproduce the problem?
1. I set the WB to 15000 15000
2. run fill (it took about 24 hrs)
3. chunks now past 560(ish) blocks are not filled and now refuse to auto generate when you walk into them, it's a straight drop to the void.

What is the expected output? What do you see instead?
expected output is chunks should be filled. which they are not.

What version of the product are you using?
WB v1.8.5 on spigot 1.9 (latest spigot build as of this posting)

Do you have an error log of what happened?
No errors were output...

Please provide any additional information below.
When I place blocks inside the empty chunks, they stay, so the world file (I'm assuming) shouldn't be corrupt...
I've tried filling again with force as "true" to no avail.