[chuckhendo]

I literally just tried this in Safari 10.1.1: https://codepen.io/chuckhendo/pen/NgGZqg

Maybe it affects older versions of Safari, but I don't recall having run into it.

"backdrop-filter" is irrelevant - it's an entirely different feature.

[colept]

It works now I guess, but Safari has quirks I've seen time and time again where things don't work as they should.

I'm also hesitant to call it "fixed" considering it happened just last month and YMMV with a one-element pen.