Abandoning missions was also available in Phantasy Star Universe, however there was no reset in that game any you could keep doing the mission over and over as many times as you like. This is nothing new. Im sure the developers are aware of this loophole and if it was an issue they could nerf it server side without having to issue an update.

Some people are complaining about crafters not having a similar 'exploit', when in reality crafters have the advantage when it comes to gaining sp by way of crafting non leve items, they have a virtually limitless source for gaining sp by crafting items in their inventory so I dont see anything wrong with this minor exploitation to guarantee you get a leve that will give good sp.