If this is an unfiltered portal and there is only one record showing in the portal, then there is only one record with a match field value that matches the match field of your layout's current record.
If you have this relationship in Manage | Database | Relationships:
LayoutTable::__pkLayoutTableID = PortalTable::_fkLayoutTableID
Then, if the value of __pkLayoutTableID for the current record on your layout is 345, only records in PortalTable that have exactly 345 in the _fkLayoutTableID field can appear in the portal.
Hmmm, also make sure that the fields in your portal are actually "owned" by the enclosing portal row. In layout mode, try moving the portal a few pixels. All of the fields in the portal should move with the portal. If they don't , they aren't part of the portal and this will result in what appears to be only one record in your portal.
To correct this, drag the field(s) out of the portal, release the mouse button and then carefully drag them back. Do not release the mouse button until the borders of your field(s) are fully inside the borders of the first portal row of the portal. Sometimes, you need to size the portal row a bit extra large in order to get the fields back where they need to be and then you can resize them back to a tighter "fit".
This worked great. Thanks for your help.