Thanks for your answers and help,
CityMonk, that is exactly the problem.
I should not contract the pelvic floor when I do chest breathing, but I just cannot stop it. I am not intending to do mulabandha.
I am getting into the root of the problem. I have very tight pelvic floor muscles, with too much tension in the muscles as a result of that.
The pelvic floor is connected to many nerves and muscles, like the abdominal muscles, and I don't seem to be able to work on one part without pulling from the other.
I have to learn to relax or extend that part of my body. All practices that contract the abdomen, like mulabandha, are not good for me.