Thank you for your post.
I am unable to replicate the issue. This is what I have done:
1. On my iMac running Mac OS X 10.11.6, I launched FileMaker Pro Advanced 15.0.1 and created a new database file.
2. In Layout Mode, I added a Popover button. I copied your text block and pasted it into the Popover panel. The bold
"major name" displays as expected.
3. I closed the Popover, saved the layout, copied the Popover to the clipboard, created a new layout, and pasted the Popover button to the new layout. Opening the Popover, I see the text with "major name" only in bold.
Let me know what I am doing differently than you so I can reproduce the issue.