This is noticeable in particular with something like content: "x" url(x) / ""; A test for this has been added here: https://github.com/web-platform-tests/wpt/pull/44971. This is somewhat tricky to fix as the current code for this in AccessibilityNodeObject handles this and the img element at the same time apparently.
<rdar://problem/124267497>
Hmm, I must have been mistaken yesterday when I thought this change had an effect. It's not needed after all.