So that is annoing and started just recently, was not there from the beginning of the game. When I deselect my main Character as the party leader, (for example because a other party memeber has better skills to negoiate with other NPC's, and then move on, the main character stops following the party. I have to separate him from the party chain, selct him then and move him on to the party.
The game is practically not playable anymore once I select a different party member as party-leader. So annoying.