Okay, on level 4 you may either increase 2 attributes or do another selection.
For my fighter I tried that and checked the selection where you gain 4 weapon proficiencies.
I got quite confused because weapons were listed in which I'm already trained.
So I selected e.g. longsword again, but couldn't see any difference in stats afterwards.
So, is being able to select weapons which your are already trained in just a bug, or does it actually do something which I missed in the attack bonus and damage overview on the character sheet?