Well, for yesteraday's picture I wrote: "for a reason or another all of the smoke was not running into the chimney". Today I went on inspecting further. I opened the lid of the stove, and realized that inside there was a lot of soot stuck on the walls. And that much soot hinders the flow of air inside the channels of the stove. So no wonder there were problems. I wiped most of the soot away with an old brush. After that I lit a fire - and now all the smoke was going into the chimney. Great!