Bug and solution: Aperture 3 adding unwanted border to prints

Just ran into a strange bug in Aperture 3: unwanted borders on prints. Turns out this seems to be caused by a corrupted preset. Here's the situation:
I was trying to print an 8x10 on letter size paper, which means the photo would obviously not be borderless. It was a portrait shot on a white background and this is what Aperture gave me:

not so seamless...

See that grey line on the left? Not supposed to be there. Fortunately I realized this bug was also visible when hitting the Preview button in the Print dialog, so I only lost one physical print. I fiddled with various settings for about 20 minutes before finally deciding to try starting from scratch, with the built-in Standard preset as starting point. It worked. I duplicated all the settings from my old preset and voilà… No more lines!

Just for fun (meh) I then tried simply duplicating my old 8x10 preset: no go, the bug reappeared.

So, at some point custom presets got messed up. Since I usually print borderless I probably didn't catch it right away. Hopefully this won't happen too often — it's a bit of a pain having to re-create everything.