I have a set of polylines which have previously existed separately, but which I've joined together at end points to form 1 polyline using the [join] command. I've made the global width fairly massive, for the purposes of the drawing I'm doing.

At the corners - the points at which the previously separate lines have joined, it still looks as though they're separate. the line has a sort of a kink in it. It wouldn't be visible if the global width wasn't so large. I hope that makes sense.
 
I wondered is there a way of making the whole thing, appear as one line, with proper corners. This happens when you draw it all in one go but not when you form a line from joining.
 
Thanks for any advise.

If it's a continuous linetype, there should be no gaps/kinks at corners.
 
Any other linetype, you get kinks.  It must not be any easy fix by Autodesk because users have been unhappy with this forever.