Ok after many years of using wblock, the newer users finally convinced me to use copy and paste instead. To be honest I like copy and paste in the newer versions because of all the options (paste to original coordinates, copy with base point, etc.)
But I just tried copying a centerline from a drawing and pasting to original coordinates in a new drawing. Now I can't join the entities into a polyline. They can be joined in the original drawing.
I used the wblock command to create a new drawing from the original entities. I can join the entities into a polyline in the new drawing created by wblock.
Has anyone else seen this behavior?
I see this behavior in 2006 and 2007.
I posted the drawing here if anyone wants to take a look at it.