I too am having trouble with this. I'm going to give this old post a bump and hopefully get an answer.
I've tried adjusting the preferences to "connect dashed lines with spaces less then ____" with no avail.
I've read others are just tracing the lines and creating native VW objects. I would rather the import function do this as there are many lines to be re-drawn otherwise.
I am importing .dwf into VW 2016.
TIA