I did manage to temporarily, of not permanently, fix the problem by exporting the mesh as OBJ and importing it again. The skin modifier I added set all the vertices to "1" on the weight table, even when the small rings just surrounded the bone. Resizing the rings had no effect. I cleared the weight table (giving them all 0), but the rings wouldn't affect any vertices, when I resized them. Painting the weights did work, but apparently only for one bone. When going to the next bone, it has no effect anymore. So I'm a bit on that stage at the moment!
EDIT: Adding all the bones you have (or need), instead of weighting one and one, to the list, will fix the selection problem.
EDIT 2: No, not anymore...
EDIT 3: Dear googler: FIX: Weight table: CTRL A and unhook either "M" or "N" (try both, but I had to remove M) with right click, and could edit envelopes after that.
Actually, after answering all my own questions...
I have a real question. Should I use IK solvers in animation? Like, I don't know what to do, structurally or hierarchally with IK solvers, in the vehicle equation. How do I treat it?