I think this is a nonsensical restriction seeing as dummies already can't be placed near one another. Can it be changed so that dummies take damage properly? Even if, heaven forbid, someone took dummies with them to their afk training spot at abyssal demons or whatever, wouldn't they be fairly restricted by inventory space? And what would be so wrong with that anyway? The problem I would see is if you could place 50 dummies on one square and squish them all with ice barrage, but you can't do that so...
Well actually, it's better this way believe it or not. The thing about combat dummies other than the exp from beating them down is targeting. If you do afk aoe combat with them, the longer they stay alive, the less time your character spends switching targets (there's a delay to it usually, unless a monster hits you the moment your global cooldown wears off), and the more time you have doing aoes at the optimal direction (assuming you place the dummies properly), so that you hit the most amount of targets! > )
"As for forktails, bait them thusly: pound a stake in the soil, bind a goat to it, then hide ye in nearto shrubbery posthaste."
Ok, so a dummy placed properly can provide a method to constantly attack in a given direction without changing targets and losing a few ticks. I guess that does make sense. So then how about a different solution than disabling the abilities, like how about restricting where they can be used to "bank areas"?