Repro:

1. Go to https://example.com
2. Open the console and run:

(async function() {
 const cache = await caches.open('cache');
 cache.put('k1', new Response('r1'));
 cache.put('k2', new Response('r2'));
 cache.add('https://enable-cors.org/img/cloud-download.svg'); 
 cache.add('https://enable-cors.org/img/browser-2.svg');
})();

3. Go to the Application tab and drill into Cache Storage / cache
4. Click around on the 4 entries

Expected: As each entry is clicked on the response preview updates

Actual: The resource only updates if the real entries (the SVG images) are clicked on. For the synthetic responses the preview doesn't change (stays blank if nothing was previously selected, or shows the last non-synthetic response preview)