Dragonair evolving only after trainer battle?

Question

I saved just before reaching lv. 55:
First & Second attempt: defeating wild Pokémon caused Dragonair to level up, but not to evolve.
Third attempt: defeating a trainer caused Dragonair to level up and evolve.

FireRed/LeafGreen

Comments

Why did you hide my comment? I didn't think I said anything inappropriate or offensive. All I spoke about was a glitch...
I'm sorry if I offended you or anything :/

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It´s not like that, don´t worry, your comments are absolutely fine. I just wanna keep it easy to keep track on what´s happening, since it seems that this question will remain unsolved for some time...

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Oh ok thanks! Hm.. I looked but I haven't found anything regarding your question..
Maybe its a glitch?

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I would dislike that very much, although it seems there are no other explanations.

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I guess I can try listing the possibilities.

1. Accidental push to the B button (unlikely)
2. Here's something similar that happened to me (very unlikely, but I'll give it a shot). Since I was battling a wild pokemon, I was not confident that it will level up. I wanted it to hold a Lucky Egg just in case, but I gave it an Everstone instead (yes I actually did that xD) and it didn't evolve. Doubt anyone else makes that error though...
3. A glitch

Answer 1

This is most probably a glitch

Dragonair evolves into Dragonite at Level 55, regardless of whether it has leveled up from Rare Candy, Wild Pokemon or Trainer Battles, etc. Unless you have pressed the B button accidentally or given it an Everstone (which I highly doubt) then the only explanation is a glitch.