Hmm... I don't know. At least it isn't serious like a wiring problem if it isn't inhibiting their performance. Most likely it has to do with the light's molding capturing too much moisture when exposed to condensation. As for how to remedy the problem, no clue other than the obvious (ordering a replacement). Chances are though, since you already have factory standard lights the problem might stem from a faulty design in the light's mold itself (not familiar with the FTO's history).
Another thought, next time they fog up... try keeping your highbeams on for an extended time afterwards and let them "dry out" so to speak. You can even place a sheet of tinfoil over them if you want to accelerate the process as the reflection will increase the air temp inside the unit. Shouldn't take long for any moisture buildup to evaporate and (in theory anyways) should clear up your problem, albeit temporarily.