it's not, Jar. I've tested in older versions of MC (Ex: 1.2.5, 1.4.7) and this effect is not present.
I'm thinking it's something with DXtory
Happened to me too, but my whole Computer crashed instead.
I noticed this too. I think Mob And Monter are just replacement mobs to start building off of when someone starts to make a mod. A Spawner called 'Monter Spawner' Is obtainable Via MCedit, but it wont do anything. Considering its trying to spawn an Invalid entity.
This Is Very Intresting.
This is because of Mojang removing numerical item IDs. Try /give @p command_block