Render distance @32, freeze by spamming: "The save is being accessed from another location, aborting"

I get a lot of odd behavior when I set my render distance to 32. When I generate a new world with render distance set to 32, the development console says that the spawn area has generated, but I get stuck on the "Downloading terrain..." screen for a very long time. When the world does finally load, only a handful of chunks have generated (screenshot attached). The rest of the world is empty. I can even fly down the sides of the generated chunks and into the exposed caves.

When I save and close the world, I don't get any errors. When I try to re-open the world I get the following error a few hundred times.

[19:28:34 INFO]: Client> [19:28:34] [Server thread/ERROR]: Couldn't save chunk; already in use by another instance of Minecraft?
[19:28:34 INFO]: Client> aqa: The save is being accessed from another location, aborting
[19:28:34 INFO]: Client> 	at bpc.c(SourceFile:65) ~[14w30b.jar:?]
[19:28:34 INFO]: Client> 	at apv.I(SourceFile:2589) ~[14w30b.jar:?]
[19:28:34 INFO]: Client> 	at beo.a(SourceFile:107) ~[14w30b.jar:?]
[19:28:34 INFO]: Client> 	at qj.b(SourceFile:164) [14w30b.jar:?]
[19:28:34 INFO]: Client> 	at qj.d(SourceFile:235) [14w30b.jar:?]
[19:28:34 INFO]: Client> 	at qk.c(SourceFile:185) [14w30b.jar:?]
[19:28:34 INFO]: Client> 	at net.minecraft.server.MinecraftServer.y(SourceFile:582) [14w30b.jar:?]
[19:28:34 INFO]: Client> 	at net.minecraft.server.MinecraftServer.x(SourceFile:514) [14w30b.jar:?]
[19:28:34 INFO]: Client> 	at cwk.x(SourceFile:138) [14w30b.jar:?]
[19:28:34 INFO]: Client> 	at net.minecraft.server.MinecraftServer.run(SourceFile:430) [14w30b.jar:?]
[19:28:34 INFO]: Client> 	at java.lang.Thread.run(Thread.java:695) [?:1.6.0_65]

The behavior after this is a bit erratic. Sometimes the world loads, and sometimes I get nothing but void.

I've attached a full copy of the errors in the development console.