Once in a while I see this error in console

17:03:24 [WARNING] [Lift] Task #34 for Lift v29 generated an exception
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:839)
at java.util.HashMap$KeyIterator.next(HashMap.java:874)
at net.croxis.plugins.lift.ElevatorManager.endLift(ElevatorManager.java:179)
at net.croxis.plugins.lift.ElevatorManager.run(ElevatorManager.java:268)
at org.bukkit.craftbukkit.scheduler.CraftTask.run(CraftTask.java:53)
at org.bukkit.craftbukkit.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345)
at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:529)
at net.minecraft.server.DedicatedServer.r(DedicatedServer.java:222)
at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:493)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:426)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:856)

Duplicate of previous bug. And fixed for version 30