Client crashing when right clicking unequipped leg armor

User trys to right click some leg armor when its not equipped, the leg armor then equips to the chestplate slot in the armor inventory. The user then crashes.

2013-02-02 16:13:01 [WARNING] Failed to handle packet for USERSNIP/IPSNIP:
java.lang.ArrayIndexOutOfBoundsException: 4
java.lang.ArrayIndexOutOfBoundsException: 4
at rx.f(SourceFile:396)
at rz.q(SourceFile:1309)
at tx.a(SourceFile:237)
at vv.a(SourceFile:103)
at jb.a(SourceFile:218)
at jf.a(SourceFile:363)
at fn.a(SourceFile:58)
at cg.b(SourceFile:349)
at jf.d(SourceFile:61)
at jg.b(SourceFile:39)
at ic.b(SourceFile:30)
at net.minecraft.server.MinecraftServer.r(SourceFile:478)
at hx.r(SourceFile:248)
at net.minecraft.server.MinecraftServer.q(SourceFile:395)
at net.minecraft.server.MinecraftServer.run(SourceFile:329)
at gn.run(SourceFile:565)