As can be seen both here https://jsfiddle.net/7wsghcn0/ (dialog) and https://jsfiddle.net/L4traqh8/ (popover), if you press open and then try to close the top-layer element using the escape key, it fails because focus is inside of a search input. Safari: Fails to close Firefox: Closes Chrome: Closes
Adding to Luke's bug here, my testing shows that this is not limited to search input, but any input type as well as textarea. It might be a general form field focus issue inside of a popover.
<rdar://problem/132678928>
Relevant code is here if you'd like to take a look: https://searchfox.org/wubkat/rev/b36cbce69fddb7da33823f316bd8ead5bebee970/Source/WebCore/page/EventHandler.cpp#4075-4083