To confirm: You see two rows of exactly the same data, not one row of data followed by a blank add row?
If that's the case, I'd enter
findlayout mode and click on each field in the portal row and check the text shown to the left of the :: in the Inspector's Display Data From box. Does this text match the name shown in Portal Setup | Show Related Records From for the portal?
My guess is that they do not and that they should. Perhaps you used Portal Setup to redirect the portal to a different table occurrence and then failed to update the fields to redirect them to the new table occurrence.
I knew it was something simple. I was trying to figure out how to discriminate between data entered from different layouts and figured it was easiest to create a separated TO for each layout, i.e. one TO for hermeticity since it uses one portal and two for X-ray since it uses two portals.
I created the new TOs and changed the portal's "show records from" but missed changing the fields on that one portal.