Hyphens on Safari: "Unsupported Property Name"

Question

From reading around this topic, I've realised that there are a lot of problems with hyphens on Safari. I couldn't find a mention of this one however.

I've designed a website with the following CSS rules:

body {hyphens: none}

@media screen and (max-width: 342px) {
    h1, h2 {
        word-break: break-word;
        hyphens: auto;
        overflow-x: hidden;
    }
}

Most of the time, I don't want hyphens, the exception being for larger titles on very small screens.

This works well on Firefox and Chrome. On Safari however, the hyphens rule is accompanied by a yellow triangle warning symbol and greyed out with the message "unsupported property name". This is weird because hyphens is apparently supported by Safari. Hyphens then seem to be applied on all screen sizes anyway.

You can view the issue on Safari with the first title on this page, where it says "Maruthappu". I also have some screenshots below.