The addon only shows everyone that has the new role tank, not just the ones that are marked in the raid as tank. Its really anoying because many people have set the role "tank" randomly. The issue exists since pre patch.

So I looked in to it on my own and the problem is this line. The first part of the if statement adds everyone with the tank role. When I delete that part and only use the GetPartyAssignment function everything works like I need it to.
But I don´t know if iam the only one with this problem, of the new roles in a raid. In groups everything works fine but as mentioned before in our raids the tank role seems to be distributed kind of random were mages and warlocks get the role tank. And because i seem to be the only one with z-perl in our raid no body really cares to correct their roles.
So I think this solution is good, because as far as I experience it in raids tanks get marked and nobody really depends on the role system for that, so I could create a pull request with this change.
There could also be other solutions without omitting the role function completely. First would be to be to check if somebody in the raid is marked as tank and use GetPartyAssignment in that case for building the tank list and only use the role function as fallback. Another one would be to add an option to not use the role function for building the list.