Well… I think you may have discovered an edge case bug. Seems the app doesn’t like the acute angle at point B2 when using the curves. I tried every possible way to create the pattern piece heart shape - with and without the mirrors, single curves with and without all the node points, and it always end up the same… the other pieces overlap the full heart shape. I also found you can’t add a seam allowance to that shape. Indicating there is an issue BEFORE one even gets to the layout stage. It’s like the shape gets turned inside out, where there is no seam allowance, and the piece becomes unselect able. I tried all sorts of paper sizes - no good. It either does the same over lapping, or if the paper size is too small - like A2, the piece disappears in the layout.
Just as a test, I made a piece with just the node points and no curves for that piece, and it worked correctly. No problem.
Made a heat shape with just a single curve and 2 control points - mirrored:
Flatten the acute angle at B2 and ta da!
And in the layout::
So it definitely appears to be some issue with the curve path… maybe with the start and end angle? Like I said good news is this is not something that was recently introduced. Bad news is I have to decipher & figure out what is going on in the existing code. I’m placing my bet it’s on a fuzzy math issue. Any takers?