We have had this since we started bukkit and can perfectly reproduce the error. We don't know if this is a bukkit or a minecraft issue. Get a item with a subtype value eg tiles/dye/wool/sapling/wood etc Tiles are the best we found to get this bug. Break something while holding that tile. The tile icon in your inv will change to the very old style tile icon and every time you mouse over you will crash. White wool turns black you don't crash though. Tiles all go to the old school icon you crash. Saps all go default tree no crash. Wood goes original don't know about crash. Dye turns invisible no crash. I have a extensive guide on how to fix it on our site for players as its always happening. We also found this which seems to be the same thing talked about. So is this bukkit or minecraft itself? and is there a fix?