so this happened. I have done practically everything I’ve done with other patterns, but I can’t figure out why these patterns suddenly overlap? anyone got any ideas?
edit: it doesn’t seem to happen in A2 size, but does in any size bigger (at least for this pattern).
Can you send your pattern (and measurements), as well as what version / build date, OS? … so I can take a look
TY
Actually if you can look at the build date by looking at the Help menu → about Seamly2D. I want to figure out if this was existing or something that is new. By the date I’ll be able to tell what changes were added, and if they are causing a new issue.
it’s the may 21 2021 version
Thanks. The good news (for me) is, it’s not because of any recent changes.
I’ll take a look with your pattern tonight, and see if I can see what the issue is. I have to look at another layout issue Susan encountered while testing some recent updates. I’ll let you know what I come up with.
alright! thanks for taking the time!
Not a problem… this obviously appears to be an unacceptable issue, so I’d like to fix it. 
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:
No bueno.
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? 
I’ve seen this phenomenon before. Probably an error happened when copying out the parts. Maybe the curves have not been marked clockwise? I checked your file and when I copy the parts out there is no overlap. (0.6.0.1 version and Windows 10)
Data point: in Linux at least, when I start the path with the mirrored curve instead of B2 it works fine.
ETA: I seem to remember a similar issue that showed up in the Piece view instead of waiting for the Layout view a couple years back.
Hmmm… interesting. Will have to check that tonight. Not sure why switching the order of the start point / object makes a difference. Maybe something to do with the loop checking? In any case the behavior is an issue that needs to be fixed.
I don’t think the clockwise / counterclockwise is the issue - I could be wrong, but I’ll check again.
I did the heart shape without mirroring the right half… I did each half separate, and created the piece all going clockwise - still had the same issues. There is definitely an issue - in this case at B2, and it depends on the angle the 2 curves are meeting at. It’s affecting the seam allowance, which the affects the layout. Thing is while I’m well aware of a lot of the idiosyncrasies of the app, we can’t expect new users to. For ex: Shouldn’t have to know to select the mirrored part of a curve first… it should just work regardless of the order. We’ll figure it out.
Yeah the seam allowance algorithm is persnickity. It’s probably not intersecting the outset of the two convex curves properly.
Yes, there are several cases where the SA has issues. If as @Pneumarian has said, that selecting the mirror copy first works, is definitely persnickety. I think there are also issues with sone of the edge types.
Confirmed… on Windows 10, if you select the mirrored destination curve or point A1 first, the seam allowance and layout work correctly. At least another clue to go by.
