Hit the following error after changing a large area (a mountain) into glass with //replace glass, then attempting to //undo. Part of the mountain restored and the rest remains glass. (Unfortunately we're not yet running a backup system. Lesson learned)

java.lang.NullPointerException
        at EditSession.rawSetBlock(EditSession.java:135)
        at EditSession.flushQueue(EditSession.java:353)
        at EditSession.undo(EditSession.java:275)
        at WorldEditSession.undo(WorldEditSession.java:97)
        at WorldEditListener.performCommand(WorldEditListener.java:660)
        at WorldEditListener.onCommand(WorldEditListener.java:1988)
        at PluginLoader.callHook(PluginLoader.java:482)
        at Player.command(Player.java:136)
        at Player.chat(Player.java:108)
        at kk.a(kk.java:485)
        at br.a(SourceFile:24)
        at bs.a(SourceFile:232)
        at kk.a(kk.java:61)
        at eh.a(eh.java:71)
        at net.minecraft.server.MinecraftServer.h(SourceFile:275)
        at net.minecraft.server.MinecraftServer.run(SourceFile:216)
        at cj.run(SourceFile:490)

Note: This area crosses a chunk boundary, but the part of the selection which was restored was not aligned with the chunk boundary.

Edit 2: Another interesting note: In the section which was restored, none of the torches restored (they remained glass blocks), and judging by the way the glass and restored sections touch, it looks as though the routine crashed in the middle of restoring a double chest, with one-half of the chest restored and the other still glass, and the glass continuing to the south.

Fixed.

Possible cause: I am not updated to 2.3.3 (running 2.3.2) on Beta server. will upgrade and test.