Extending surfaces has recently gotten much worse. In the attached file, I can’t extendsrf on any edge direction with any extendsrf settings. I can make the surface smaller, but not larger. To reproduce this surface, loft between the two longer curves and then trim the surface with the short curve.
yup i can confirm that, i tested your file in v7 and there it extends. seems to be a bug in v8. it was already reported and there is a tracker for it 83755
means Service Release Candidate, you can set your Rhino update frequency to this in your Rhino settings, the candidates might be less stable but you will have earlier bug fixes.