Photoshop: Polygon lasso tool now has jagged edges. Suddenly changed as never used to do this?

When using the polygon lasso tool I now get a white jagged edge? 
In order to defringe a selection I have to copy areas to exclude as they are saved with a  transparency ie glass. I remove a selection from an area image A and then defringe. I have the area removed image B and add this to image A and get image C. Here is the problem! I now get a white jagged edge when both layers are merged together? I never used to get this last week?
For reference I have Anti-alias ticked. What has changed with the software?