It's a strange situation for sure. Honestly I think Bjorn just enjoys the general lifestyle, enjoys being a part of the In Flames brand and is completely non-confrontational personality-wise. As long as some of his stuff is on the album he's happy, regardless of what Anders or Benson have done to it. I think this part of an interview around the time of the Siren Charms release says it all:
"S: What inspired ‘Through Oblivion’?
B] “It was actually something that was meant to be between songs, no vocals or distorted guitars. I’ve always had the idea of doing something in between songs, connecting two songs with something in between. But when I presented it, it was a no-go. Anders said ‘we’ll make a song out of this’ so we started working on it and it ended up being something different for us. It moves on and on with nothing sticking out, it’s like a mantra or something. It’s a very different approach to music than we normally have. Usually there’s a lot of melodies and a lot of layers and it’s fairly straight forward. When the chorus kicks in it makes total sense, it was really fun to do. The bridge after the second chorus just makes the song even stronger. It was meant as a solo part, but Anders started singing on top of it and it sounded better. A lot of small things came together to make it the way it sounds today.”