Well that's how character arcs work, no? Obi-Wan starts off in TPM as the most Jedi of Jedi. A dedicated student, respectful and obedient to his master with an unshakeable faith in the wisdom of the council. Also, a little stiff and inflexible since he's still very much the temple raised padawan, despite having been by Qui-Gon's side for going on a decade.
By AotC he's a *lot* more worldly, relaxed and sure of himself. Fast forward to RotS and he's a seasoned veteran and still respectful of the council (since he is on it himself by now), there's more of an edge of pragmatism about it. He doesn't like where they're headed, but much like Yoda can't see a way around it.
Anyway, I'd hardly characterise Obi-Wan as dismissive towards Qui-Gon. He's frustrated that his master whom he deeply respects has a habit of making things difficult for himself by constantly butting heads with the council.
The way I look at it, Qui-Gon is meant to represent the Jedi of old. Wise, independently minded, in tune with the living force and always rooted in the moment. Obi-Wan is a more of a modern Jedi. Noble, well meaning, but hampered by a slightly dogmatic attitude.
The execution was certainly very clumsy to say the least, but from a purely conceptual standpoint it makes perfect sense that he'd fall for Padme almost right out of the gate.