Android srcset bad craziness

Apparently a bunch of Android devices poop all over <img srcset>. I'm seeing nonsense in my logs where Android is trying to load the srcset as if it was src, e.g. from here it's doing:

GET /images/2017/inhuman-drywall1.jpg%20711w,%20https://www.jwz.org/images/scaled/640/2017/inhuman-drywall1.jpg%20640w,%20https://www.jwz.org/images/scaled/360/2017/inhuman-drywall1.jpg%20360w HTTP/1.1

The user agents look like

"Dalvik/2.1.0 (Linux; U; Android 8.0.0; Pixel XL Build/OPR3.170623.008)"

and so on, with the version going down to 6.0.1.

But when I run an Android emulator, it has a more traditional user agent beginning with "Mozilla/5.0 (Linux; Android 8.0.0".

What is that other crap? And how is it so broken?

Previously, previously.