Is this a bug in .iges file from MoI or not??

 From:  boatstalker
658.3 In reply to 658.2 

Thank you for explaining this issue. I have now imported several other cuts into Prosurf and this happens sometimes and sometimes not. If the residual trimming lines are joined or unioned before saving and exporting to Prosurf this doesn´t happen.

However for some reason the commands "join" or "union" do not always seem to work. For example the deck bridge on the catmaran below was constructed by a sequnece extruding, intersecting, deleting, mirroring and moving surfaces. There is a "scar" from this procedure left on the left side of the deck bridge. The scar on the right was easily removed using the "union" command, but not on the left side.

Is this some kind of a bug in the NURBS kernel library or me just being clumsy?