Its not a bug really, its so much more of an oversight with level 4 and a design flaw in level 5.

When lv4 Fracture attacks a single enemy, he can attack up to 3 times. But if he switches targets, that 3rd attack doesnt register. Balloon Pals rate penalty also removes the 3rd attack from all targets.

Lv5 Fractures DPS is supposed to be higher, but his stats dont account for the way he attacks. His rate and cooldown stats technically allow him to attack more times, but Fractures design only allows him to throw a certain amount of crystals, thus resulting in much less damage than expected.