Hmmm. That has never happened to me, but the first thing that seems to come to mind is have you really, I guess you could say influenced Carth or Mission very much? Or in simpler words, do you talk to them much?
Have you seen Bastila's 'messenger'? Ooo, the Carth 'sidequest' is actually on Korriban. So maybe thats your problem. No wait, Carth's 'sidequest' also has a messenger. Anyways, have Carth in your party when you go to Korriban.
It could also be some mods, but I have no idea what to tell you if that is your problem. Hope I was some
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