Thank you for your post.
I am unable to replicate the issue using FileMaker Go 13.0v4 under iOS 7.1.1. Here are the steps I took:
1. Using FileMaker Pro 13.0v3 under Mac OS X 10.9.3, I created a table with an ID field and a few text fields. I created a second table with an ID field and some text fields. I set a relationship between the two tables.
2. On the layout of the first table, I created a Popover button, and placed a portal into the second table showing one instance in the popover panel.
3. I sized the portal to take up much of the space in the popover panel, and adding one of the text fields, I formatted it as a Radio Button set with 26 values (one for each letter of the alphabet).
4. Behind the popover panel are three text fields.
5. I turned on Network Sharing.
6. On my iPad, I launched FileMaker Go 13.0v4 and accessed the hosted file.
7. I tapped the popover button and the popover panel displayed. I then triple-finger double-tapped the screen to zoom, and again to return to 100%. I did this more than 40 times, moving around the screen after zooming, entering data, etc., and I was never able to replicate the issue. The Popover panel never became transparent to display the information beneath it.
Let me know what I'm doing differently than you so I can replicate the issue.