Kyle may have ordered the Sampler Platter,
Yes, it does show sample data in a portal.
Sorry, I meant sample data from the current record.
Kyle may have a hard time determining 'current',
I'm sorta guessing at this but from my observations it appears that individual fields that have a related record can show that one records data. FMP figures that out OK. But the portal is a construct of all related records so FMP doesn't automatically know which one to show. I'm a little surprised that in Layout mode where there are no valid relationships that related fields show any data at all.
Since it does show sample record data if outside the portal and if you really need to see it I suggest copying the field to outside the portal somewhere and review it there.
Put it in as a feature request. I'd like to see it too.