This was the first episode to be dubbed for and aired on KidsWB.
I get it. Charmeleon thought Ash was taking it's opponent's side and supporting Paras. That's why Charmeleon stopped trusting Ash.
No, that is not the reason.
Maybe not the sole reason, but surely it helped to prompt Charmeleon's disobedience. I mean, you have a Pokemon who's much more fierce than the other ones in Ash's roster and is being told not to do his best.
Though I wonder why they didn't allow for Paras to make the first move.