Craftbukkit RB: 1.31 Plugins: WorldEdit, BukkitCompat, CoreProtect, xAuth, DeathNotifier, PermissionsEx, Modifyworld, LWC, mcMMO, WorldGuard, TreeAssist, Essentials, ChestEnforce, ChatManager, EssentialsSpawn. I can't place snow blocks, its ID 78. When I do the snow gets removed and placed back into the inventory.
Reacting because of the comment on Bukkit bug #2554 The one described in the bug goes as follows: Put something in an inventory window (the one of 9 in the bottom bar when no menu is open). Then put snow layer there. After you put the snow layer on the ground, it gets replaced by the item that was in the inventory window *before* the snow layer. (if there was nothing then air us used the same way, so it looks like you placed a snow layer and then it just disappeared from the ground *and* from your inventory) So if everything I said is *exactly* the same as the problem you have, then yes, it should be the Bukkit bug #2554