Hello Tinkerjenn,
At the moment the only XP being converted into star coins is the adventure XP. This is still a new mechanic and the devs are continuously working on this feature. We do not have any info at this time if the devs will elect to convert all unused XP to star coins upon release of the star coin system as they did with the introduction of star coins themselves. Sorry for any inconvenience this has caused.
'The Settlers Online' Support Team
This is complete and utter BS. There's now ZERO point in completing quests that offer XP as rewards. I am a VERY unhappy player.

