Why does an image with src and srcset make a redundant network request in Chrome?

Question

Consider the example:

<img src="https://via.placeholder.com/200x150"
     srcset="https://via.placeholder.com/200x150 200w,
             https://via.placeholder.com/400x300 400w,
             https://via.placeholder.com/600x450 600w"
     alt="An adaptive image 200..600px"
     />

In Chrome DevTools, I see two network requests, which is suboptimal, as I expect here only 600px version to be downloaded. In Firefox, however, the issue does not reproduce - I have one network request there. So, can it be just a browser-specific bug? Or maybe I am not adhering to some standards in this example?