How many records are in your found set? Any chance the first record is a blank record?
When you enter preview mode, FileMaker assumes you are going to use the "Records being Browsed" option to print or preview your layout and thus puts record 1 on page 1 of the preview. To see all the records in your preview, you may need to click the book icon to move through the preview one page at a time much like you use it to move through records when in browse mode.
If you only want to see the current record in Preview, you can use a script or options from the Records menu to isolate this record in a found set of just this record before you preview it.
Thanks...That does seem to be the issue. I guess I should have realized that. (Doh?!)
It's obvious after the fact, but not when you first encounter it. While not at the top of my list, I've long thought, adding the Records being Browsed / Current record option as a parameter to the Enter Preview Mode step would be useful.