Yes, I was correct in my statement. Certain types of RG58 (50 Ohm) cable has a foil shield on the dielectric with the stranded shield outside of that within the PVC jacket.

There ARE occasions that when stripping/folding back the stranded shielding a stray strand or so does not cooperate and shorts out on the center conductor and/or the foil covering the dielectric if in fact this cable contains that foil. There are LOTS of ways this condition exists and a slight shorting of a few strands of shield can throw off the SWR.

Hope that makes sense... hard to explain on a forum, but I could go into further detail if needed.