I saw many people asking the same question. But now I have solved the problem. The answer lies in defining the labels. When we define labels for each pin then we have to select material of label carefully. Though it is technology dependent and varies with the fdk/pdk. But the solution is there. So remember it would be something related to "Text" . In my case, UMC180nm, this is solved by choosing ME1-CAD-Text from the many materials available for text label. For other, it may be "ctext". There are many guessed answers in but none of them works. This is the final and practiced answer.