I experience this problem on both samsung i5500 and i5800:
Looks like height of divider is between 0 and 1 pixels, so it sometimes rounds to 0 and sometimes to 1. The picture changes if i scroll it. And if i increase dividerHeight (i tried 2px and 2pt), then it becomes exactly 1 pixel thicker: from 0px it becomes 1px and from 1px it becomes 2px, looking like a kind of wave.