Thank you for the post.
I am able to replicate on both Mac OS X and Windows with FileMaker Pro 13.0v1. The steps I took to replicate follow:
1. Created a new database file with a single field
2. Added a Pop-Over button in layout mode, placed the field on the pop-over
3. Anchored the button to the top and right
4. In browse mode stretched the window larger
5. Clicked the pop-over (pop-over displays) and clicked again to hide
6. Resized the window to very small
7. Clicked the pop-over
Expected result: Pop-over displays
Actual result: Pop-over does not display
Additionally, I forwarded a report to Testing and Development for review.
An entry in the Known Bugs List has been linked to this Issue Report. Any Comments/Questions/Suggested Corrections should be posted here or in a new thread. Please do not post such comments to the Known Bugs List thread.