I am trying to obtain a clipping of a contour map into a polygon by using the command Vector->geoprocessing tools ->clip in qgis 2.18.13 freshly installed on Ubuntu 14.04. I run the command on a contour lines layer whose files are within a directory since it is a DXF file (to be imported to autocad) and a shapefile (a polygon basically)

But when I run the command I get the message: "NameError: global name 'features' is not defined"

Is this error due to some coding glitch in the new release? What is the global name Features referring to???? Do I have to bother?

Regards