<picture> with img-thumbnail class

Created by: t5k6

I am trying to implement <picture> tag to selectively serve pictures; webp format for Chrome based browsers and jpeg fallback for other browsers. However using Bootstrap's img-thumbnail class is not working properly, it creates handlebar like artifact on border sides.

Sample code:

<picture class="img-thumbnail img-fluid">
  <source srcset="/path/to/image.webp" type="image/webp">
  <img class="img-thumbnail img-fluid" src="/path/to/image.jpg" alt="">
</picture>

Bootstrap version: 4 beta