Why did the mayor hesitate before saving Fauchelevent?

The mayor, of course, is none other than Jean Valjean, going under one of his many aliases—this time, Monsieur Madeleine. As mayor of Montreuil-sur-Mer, he cannot reveal his sordid past as a convict, or he'd be destroyed. One day, as he's walking through the town, he sees Father Fauchelevent pinned beneath his horse and cart, the only thing this once-prosperous lawyer has left in life. As the horse's legs are broken, it cannot rise to its feet, and despite the best efforts of passers-by Fauchelevent remains pinned beneath the wreckage.
Valjean's immediate reaction is to help, even though Fauchelevent, resentful of his wealth and status, has done everything he can to injure him and his reputation. After arriving on the scene, it's obvious that only Valjean has the necessary strength to be able to lift up the cart, thus allowing Fauchelevent to be saved. But Valjean initially hesitates. The intrepid Javert makes yet another of his unwelcome appearances and says that he knows of only one man capable of performing such a feat of strength, and he was a convict. Although Valjean is understandably reluctant to reveal his identity, he tries his best to ignore Javert's presence and lifts up the fallen cart, thus saving Fauchelevent from almost certain death.