What issues does it have?
As far as I can tell, Ninja's Dream within a Dream and Blue Mage's Matra Magic (I can't think of any other multi-hit-on-one-target abilities) work fine. I don't think too many people would raise a stink if the Blue spell were janky (Other Blue spells like Diamondback have had slidecasting jank for a long time), because dps usually doesn't matter as much if you're bringing Blue Mage, but Ninja's a normal job. If some netcode peculiarity was causing problems with Ninja's damage, that'd be a pretty big bug like the one we have with pet potencies not benefiting from traits, which the devs are looking into now.