I've noticed in Arboria that if I have two characters using ranged attacks (Monk uses his Deadlyrang and Warrior using the transferred Sword of Zar) when there is a single group of monsters not in melee range, that the opposing group just sits there and does nothing. They don't advance. They don't cast spells. They just sit there and take it. I've tried it on several different groups of craetures in various dungeons there, and it's consistent.

While it's a nice trick to help regenerate spell points (taking the place of the Party Attack exploit), it's almost certainly a bug.

Edit - It also works if the group of monsters is within melee range, at 10' away.