here is preview mode
Are these repeating fields on this layout or is each row a single field?
Is each row a different record?
Each row is a different field, not repeating pure text fields.
All one record. I have this setup working many other places and have never seen this jump before.
Are the fields set to slide up?
When I take a closer look at your screen shot, no extra return has been added. Instead, the font metrics are different and thus the text inside the middle right field wraps to an extra line in one case and not the other.
And a search of the Known Bugs List pops up a report matching that issue:
For More Information see: FM 12 preview mode issue
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: https://www.dropbox.com/s/jt09b82i0xijbu3/FMP%20Bugs.zip