Yes, it is, although it exists to a limited extent on XP. (XP: C:/Documents And Settings/whoever, Vista: C:/Users/whoever)
Do you have administrator privileges on your computer? (I think you do, since you were able to install Blockland or whatever, but I can't think of a reason for the ban list breaking)
Also, it's possible that you have a broken client-side Add-On, which automatically runs when you start the game and isn't disabled in the Add-Ons menu.
EDIT: What is the 'Self Damage' option in minigames supposed to do? Even when I've disabled it, I can still damage myself by firing rockets at my feet and when it's enabled, firing a gun then warping into its firing line doesn't hurt me.