Product and version FileMaker Pro 16.0.1
OS and version MacOS 10.12.5
Hardware MacBook Pro (Retina, 15-inch, Mid 2014)
Description & How to replicate
Add a button on a given layout
Add a popover next to this button
Add a content higher than the popover to the popover so you need to scroll into the popover to see the complete content
Adjust the popover to make it overlay the first button
Open the popover and move the cursor at a place above the first button
Try to scroll the popover content. You can't.
If you move the cursor outside the (hidden by the popover) button you can scroll.