Loot allocation seems to not work as intended

Hi devs and players,

I seem to have difficulties with loot allocation. Free for All allocation seems to be wonky OR (maybe) I haven't all the knowledge to understand.

Story :

With a friend, we began a new duo to play the game in Standard league, for him to discover the game further with a new class and all.
- Short allocation was the default setting, so we played like this like 2 hours.
- Then I changed it to "Free for All" because he left and I stayed a while (and listen... oops wrong game !) to try things... I thought it would be better to just pick everything we could without 5 sec wait time.
- Next game we went to finish Act 2, and I was proud to tell him that now we can just pick things up and exchange them later in town if one or the other picked an item that could interest each other without the "oh you left this or that on the floor" feelings.
But...

Problem :

In fact first hour was cool, but at the end we emptied temple to finish leveling and kill the boss then go Act 3 until next game. And some rare items and currency, and some other things, went grayed out and available only after the 5 seconds... I had Free for All, and was the party master. I don't understand why.

Disclaimer :

I read here some topics about that allocation system to see if people have the same problems. I found interesting technical information, but nothing that indicates I'm wrong about my thinking :
- Allocation changed on the fly can only be applied to new instances : Checked (for Geek's God's sake, I changed it days before beginning playing again),
- My friend changed it when I told him, just before entering the temple before the boss zone, and after that, Act 3, the problem was still here, when we killed the guards molesting Clarissa, rares items were allocated to him, and some to me as he told me he couldn't click on currency and yellow items.

I mainly let him take all currency items because I have so much that I prefer let him take them, but sometimes he just can't and leaves them behind so I didn't understand why.

Sorry for long post, I may just be an idiot who believes he understands all but in fact not. So don't blame me please.