Bukkit

2.5.7

• Fixed the ConcurrentModificationException, fixes Ticket #368 and #378
• Fixed the misspellings of Messages, fixes Ticket #371
• Fixed, kind of, NullPointerException when a player joins and there is no cell, fixes Ticket #364
• Fixed jail not sending players who are mounted on something to jail, fixes Ticket #351
• Fixed /jailset not ignoring the casing, fixes Ticket #338
• Fixed the /jail command not working at times, fixes Ticket #372

From 2.5.5

• Numerous bug fixes (including JoinEvent NPE and PreProcessCommand NPE)
• Added JailVersion Command
• Begun adding Handcuff Command
• Changes to some Messages to make them more clear.
• Tried to improve Jailswear
• Jail command no longer allows you to jail players who are already jailed!
• Started adding support for Scoreboards

Player inventory is not handled the best possible route that it can be, except weird things to happen there and armor contents only being half saved. That will all be fixed in the rewrite of the plugin.