After checking the pattern, I understood where the confusion came from: the pattern pieces are correct but it would be easy to get that difference in length if you didn’t sew the bias binding just as instructed.
So let’s see how you should attach the bias binding on the Xerea dress neckline.
Here is the illustration for this step in the instructions booklet. The instructions tell you to “finish the neckline with bias binding: with right sides together, pin the bias binding to the neckline matching the edges. Stitch on the first fold line. Fold the bias binding to the inside twice and edgestitch.”In pictures, this would look like that:
The bias binding is stitched on the inside of the neckline and is now invisible. This will give you a very narrow seam allowance around the neckline and the back yoke seams are matching correctly in the back.
Pin the bias binding to the neckline, matching the raw edges. I like to pin it to the wrong side but this is a personal preference, you can also pin it right sides together. Stitch inside the first fold line crease. Fold the bias binding over the seam allowances to cover them and edgestitch (make sure your binding covers the first line of stitching you did). This would look nice with a constrating color binding.Please let me know if you have any questions.