have you 'allowed creation of records' via the relationship between the layout table and the portal table?
resize the fields a bit (smaller), to make sure that they are completely *inside* the portal row. If this won't help, try creating a new portal on a new layout, maybe using another theme
Assuming that this is FileMaker 12 or newer, enter layout mode and move the portal a few pixels. The fields should move when the portal moves. If they don't, that would be your problem here.
It seemed to have happened when I moved the portal within the layout.
I recreated the portal and it's good as gold now.