I just typed a lengthy reply about my experiences with wetting agent contamination, but then re-thought the problem ...
these marks on tinm@n's pics are lighter in the positive, so they are darker in the negative, and are therefore developed more than the rest of the frame. Also, it has affected the filmbase+fog, making the fb+f lighter in those areas. I would suspect some kind of light leak .... or maybe not ....
the problems caused by wetting agent residue (which is not always sticky and obvious, often there is no perceptible residue visible) cause air bubbles to form around the sides of film and dev reel. These are nearly impossible to shift, no matter how hard you rap and bang the tank on your desk/floor/anything else, and result in under-developed areas around the frame edge (eg lighter on the negative, darker in the positive). these do not affect the film rebate though because this should not, at any time, be receiving any light that would affect the film emulsion in this way. FB+F should be uniform across all the unexposed areas of the film.
so .. maybe a lightleak somewhere along the way ... maybe a flaw in the film (are you getting this problem across several different types of film? Possibly a fault in your dev tank letting a small amount of light in? POssibly even a winding problem with the film roll ... perhaps the spooling mechanism in your camera isnt tensioning the roll enough allowing small amounts of light in through the edge and paper-backing?
It may be a different problem, but that is where I'd start if I was getting over-developed areas with such immediate transitions to normal developed areas like this.