Dispel not working as it should

The attached screen shot is from skeleton king and it is supposed to remove 96% of removable buffs. After watching tons of fights with players that have astromancer the supremacy that she casts is almost impossible to remove which is not correct because her skill is a removable buff, astromancer does not have no debuff skill like skeleton. How can the supremacy consistently remain active with a 4% chance of not being debuffed? given the 96% removal of removable buffs it should be rare that this buff remains intact. I have know idea how the makers of the game arrive at such silliness.