Thank you for quick answer. This might be the case, but V500 uses LED source. Also, I tried on both kind of papers: OBA rich satin (Tetenal) and oba free baryts (Tecco). What I can try is to take a picture by digital camer instead of scanner in my studio flash lights - what do you think?
One more thing to add: when I print the 21 step wedge target again but with linearised profile the printout is perfectly linear, so the procedure does its job but mistake is somewhere hidden...