Hebrews 5:188 does not imply that Jesus was disobedient. Philippians 2:8 (ESV) reads,
And being found in human form, he humbled himself by becoming obedient to the point of death, even death on a cross.
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".