It is not the first time i notice that i roll as ‘‘Greed’’ on item that i am 100% sure i selected “Need”.
Just 5 min ago from writing this post, i selected Need on a healer item( my loot is set correctly - to my heal spec) but i still said ‘you have selected Greed’.
So i am sure i am needing for my main spec - this is not the problem.
Are there some special rules/mechanics in MoP, or i am missing smth?
Maybe someone else has noticed this?
You can only need items for your ACTUAL spec in dungeon.
For exemple, if you are a Prot Paladin in the dungeon, and a Healer Paladin item drop, you can vote need it, but if a Healer paladin is in your group and vote need it too, you need roll “disappear” and only him can have the loot if he vote need.
Some of these choices made by the game are really questionable, though. I was erased from the roll on a sta/str/crit/expertise neck on my prot warrior. Both crit and expertise are useful stats for prot, especially in an offensive-oriented gearset. But I guess they have to draw the line between what’s a dps and tank item somewhere.
Thats true that you can only “need” on items that fits your spec and role, but not only in dungeon. I was in a group on the Operation Shieldwall dailies and i found a purple shield in a mob, the whole group pressed the need button on it without hesitation (bunch of ninjas), and it was rolled only for the actual warrior with protection spec. He stolen a purple BoE item that i found 
Well, i can tell that i never ninja ‘need’ items, or maybe i just dont understand how the system decides which item is appropriate to a specific class/spec.
Here is an example: (https://imgur.com/a/L1B8Io1)
Int+Spirit ring, i assume is appropriate for MW. I am 100% certain i pressed NEED, but the system still marked my roll as ‘greed’.
And this is not the 1st time it happens