The default behavior is to convert paths to polygons on reading the layout into Calibre DESIGNrev.
To keep paths from being converted, do one of the following:
A) In Calibre DESIGNrev use File > Open Layout with Options, then unselect "Convert paths to polygons" before using OPEN.
B) Set the following variable in the local .calibrewb_workspace/preferences file prior to invoking DESIGNrev.
See the "Controlling the Data You See" and "Defining User Preferences" setions of the Calibre DESIGNrev User's Manual.