We're aware of this...it has to do with having a custom map for some reason... We'll look into it further. Until then, if you find a person using a summoning sack in FM, please report them. Otherwise, alert a GM to kill the mobs. FYI people, if you use a summoning sack in FM you will get banned. Spread the word.
This really needs to be fixed, i've died like twice in a week. 20% on a level 150 mage is like 45 minutes at skeles....