Thank you for your post.
I am unable to replicate the issue. Here are the steps I took:
1. I created a new database file (Main.fmp12) with two tables, Main and Portal. They are connected via a number field "ID". Main has a text field Name, and Portal has a text field Phone. The relationship allows records to be added to Portal.
2. On the Main layout, I created a portal into "Portal", displaying Phone.
3. I created a record with name "TSGal", and added three portal Phone values.
4. I created another record with name "Chris", and added two portal Phone values.
5. I closed the file, transferred the file to my iPad, launched FileMaker Go, and opened the transferred file.
6. I added a new record with name "AAA", and added five portal records. At no time did I see records for "TSGal" nor "Chris".
Let me know what I'm doing differently than you so I can replicate the issue.
Did you test on an iOS 7 device? (That's the difference I noted when I first read this one...)
I tested this on both an iOS 8.2 (iPad 3) and iOS 7.1.2 (iPad unknown generation). Both results were the same.