I have a set of 2 in 1 aluminum step-ladder/ladder which I'm currently using while refurbishing my stair well and hall way. The ladder is topped off with two black rubber(?) bumpers designed to protect the surface on which it is resting. Unfortunately the rubber seems to act as a paint softener when rested, even lightly rested, against any painted surface of emulsion walls or water based paint on woodwork. It doesn't matter if the paint has been applied days or years before. It leaves a black mark which is firmly embedded in the painted surface and cannot be removed with vigorous rubbing with a damp cloth with detergent or de-greaser.
My solution was to cut down a pair of old thick socks and cable tie them over the rubber/plastic bumpers.
The ladder is around 15 years old and the bumpers still feel reasonably hard and not sticky but I assume that something is leaching out of them that quickly attacks some paints.