Leaving a raid after rolling forgoes your roll

Apparently people are saying if they roll on an item and then leave a raid your roll doesn’t count and whoever is left in the raid that rolled also gets the item instead.

I thought these items would just be mailed to you if you won and didn’t sit around waiting for everyone to roll? Bug?

Which difficulties are you talking about? I know in LFR, if you roll and leave you can still win and get the items in the mail. I’ve had several LFR drops show up in the mail later already.

Idk apparently it must be on normal and above I guess.