I have in my Hoenn team 3 pokemon with those moves (Aron with protect, Treecko and Sableye with detect) and got to May's battle in Lilycove. I had my Aron out, she had Wailord out.

 

Wailord used dive on the first turn, so I used protect in the second turn before it hit me. Turns out it still hit me, with protect on (didn't fail). I thought that protect could have missed somehow, so I switched to Sableye when Wailord used dive again. With Sableye's first turn I used detect to block dive, but I still got hit by it.

 

Later on I fought a trainer that had a Wailmer that used bounce, so I switched to Treecko to use detect and kill it. When I used detect, bounce hit me. And the same thing happened when I fought a wild Relicanth using dive.

 

It seems that protect and detect won't work when the enemy uses 2-turn moves (or atleast some of them, I can't test them all).

Bump.

 

Honestly, I forgot about this bug. Came back here to bump after I saw someone else asking about this.

Hello GreenEyedNeUn,

 

how sure are you about having 100% success rate on protect. Each time you fail a successfully used protect it's chance to work will be halved. Let me know if this is helpful.

yes it's bugged but I would say the bug is on 2-turn moves rather than on protect

heal bell fails too

https://www.pokemonrevolution.net/forum/topic/90881-url

Edited April 21, 20188 yr by hahahaka

Similar instance.... Boss Brock's Steelix used dig on my ferrothorn and I would use protect turn two during the dig attack and it would still hit me. It was not after using protect the turn before, so that wasn't the problem... also, it happened more than one time.