Harriet Hargrave, author of the Quilter's Academy series of books, calls it "fanning the seams," and she describes the process this way:
1. With the four-patch wrong side up, position it so that the seam you just stitched is parallel to you (running left to right). You will notice that the top left square has no seam allowance pressed onto it; neither does the lower right square. We are going to push the horizontal seam toward these 2 squares, splitting the stitches in the center.
2. Twist your thumbs slightly while you do this, and the stitches in the seam will release, allowing the seam allowances to lie in 2 different directions. You should get a tiny four-patch in the very center where all the seams meet.
While I can't say what's causing your problem, I hope Harriet's instructions will help you!