It is not normal, if the baseboard was installed properly. It was more of a problem with cast iron baseboard that did not have a relective paper installed behind it with a wood trim sealing the junction with the wall. But even fin tube can have the problem if the air has room to circulate behind the enclosure and carry dust with it.: the walls above the baseboard have soot like marks up to the ceiling. Is this normal? If not, how can it be fixed. Thanks