I'm running CraftBukkit 1.4.7 R1 and PreciousStones 9.5.6-SNAPSHOT
when a player leaves the field with leaving-game-mode: survival
i get this:
2013-02-15 07:23:13 [WARNING] [PreciousStones] Task #379 for PreciousStones v9.5.6-SNAPSHOT generated an exception
java.lang.NullPointerException
at net.sacredlabyrinth.Phaed.PreciousStones.managers.EntryManager$2.run(EntryManager.java:460)
at org.bukkit.craftbukkit.v1_4_R1.scheduler.CraftTask.run(CraftTask.java:53)
at org.bukkit.craftbukkit.v1_4_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:344)
at net.minecraft.server.v1_4_R1.MinecraftServer.r(MinecraftServer.java:521)
at net.minecraft.server.v1_4_R1.DedicatedServer.r(DedicatedServer.java:224)
at net.minecraft.server.v1_4_R1.MinecraftServer.q(MinecraftServer.java:485)
at net.minecraft.server.v1_4_R1.MinecraftServer.run(MinecraftServer.java:420)
at net.minecraft.server.v1_4_R1.ThreadServerApplication.run(SourceFile:849)

The other thing i want to notice:
entry-game-mode and leaving-game-mode work only on other players and NOT the owner of the field. If it is an intended behavior, maybe you could suggest something to override this...
I have no-owner: true and it doesn't helps.