The Poser's answer :

"This will happen when there are multiple figures in the simulation and the cloth has vertexes in the Constrained group. When there is more than one figure in the simulation Poser needs the clothing item to be parented to the figure so it knows what the constrained vertexes are supposed to stick to.

• Select the clothing
• From the top menu choose Object > Change Parent ...
• Select the hip or chest (or really any part) of the figure the clothing is for.
• Recalculate the simulation."

Indeed the solution is to parented the dress to the character before doing the simulation, I owe an apology to all those who gave me this astonishing solution that I did not know about and indeed it works. This happens because the bench is a figure and not a props. Now I'm waiting for Poser's answer to find out what has changed in Poser 13 because there doesn't seem to be this problem with Poser 11 and 12.