Yes, the third measure. In the Mule edition, there is also a double sharp on the G in the fourth measure, but I'm not troubled by that. Carvingcode's theory is interesting ; hopefully a oboe player can tell us wether the marking would make sense for a oboe.This does not appear in my edition (Schmidt, ed.).
Do you definitely mean the third measure? Because there's a a double sharp on the G in the fourth measure.