Polymarker vanishes when histogram is large

The situation is as follows:
I have two histograms superimposed on each other. The first one is plotted with the default plot options and is a, more or less, continious line. The x-axis is a couple of thousands bins wide. The purpose of the other histogram is to “point out” certain bins, so it plots a polymarker at these locations (ON the line). The problem is that when the x-axis has more then about 1000 bins, the polymarker vanishes! Does anybody has a clue why!


Can you send a smal example showing the problem ?