In Hebrews 5:8 it says that the Son "learned obedience" through what he suffered. Does this imply that he was disobedient at some point, or is there another way to understand it?
Hebrews 5:8 does not imply that Jesus was disobedient. Philippians 2:8 (ESV) reads,
Both of these verses teach us that it was God the Son who had no need of obedience before becoming a man. Once he did become a man there were things that for lack of a better way for our minds to understand it, he "learned" or was "becoming". He was always the perfect obedient Son, but in fulfilling all prophecies, including suffering on the cross, Hebrews 5:9 continues to say that he was "made perfect". Which in keeping with the thoughts of this question does not mean that there was a time when he was "imperfect".
The steps for determining a solution are these:
The Scriptures do not Self-Contradict
Disobedience of parents would be sin.
Disobedience of legitimate authority would be sin:
Since Jesus is without sin, he was never disobedient.
This shows that what was lacking, which he needed to learn was not disobedience.
Alternative Solutions from Within Scripture
He lacked experience being obedient when his will was different than that of the Father since normally they were in complete agreement:
The Logos who was God became flesh, that is, he became visible in flesh (John 1:1,14; 1 Timothy 3:16). Jesus experienced obedience in actuality because as God he neither experienced obeying as man nor experienced suffering, for he only knew these things, but to do them in actuality is indeed a learning, i.e. experience.