So does nobody have any suggestions on stopping the lines happening? I came across 2 so far:
1) don't send the folder through completely but bring it back out the way it went in to stop the bottom line, then you can make a feature of the side lines. This worked when I tried it but you have to get used to how far through to send the folder.
2) put a thin piece of scrap card around the edges but not over the pattern. Not tried this yet, it seems a bit of a faff to be honest.
The crafter formerly known as "the crafter formerly known as Blarf"! Ha ha!