Ligatures being applied in iOS's Safari but not on OSX's Safari or Chrome

Question

I'm using the free version of PT Serif loaded through Google Fonts, and for a while I thought it didn't had the common ligatures. Until I launched my website on the iPad and found out that it was correctly rendering them. Upon inspection, it seems neither Chrome nor Safari for OSX are rendering them correctly. Chrome for Android is also ignoring them.

Here's a render on Chrome v45 on OSX El Capitan:

Note the fi in breadth-first search. Now on iOS:

Here's the relevant CSS:

font-family: 'PT Serif', Georgia, Times, 'Times New Roman', serif;
font-size: $base-font-size;
line-height: $base-line-height;
font-weight: 300;
-webkit-text-size-adjust: 100%;
-webkit-font-smoothing: antialiased;
-moz-font-feature-settings: "liga=1, dlig=1";
-ms-font-feature-settings: "liga", "dlig";
-webkit-font-feature-settings: "liga", "dlig";
-o-font-feature-settings: "liga", "dlig";
font-feature-settings: "liga", "dlig";
font-variant-ligatures: contextual;

The font is being loaded in the page header using the following code:

<link href='http://fonts.googleapis.com/css?family=PT+Serif:400,700,400italic,700italic' rel='stylesheet' type='text/css'>

You can check the aforementioned webpage here.

Is this some kind of limitation, bug, or is my CSS missing something?

Answer 1

It seems Google Fonts is the culprit. Substituting with Brick, I get all the ligatures I was looking for:

<link rel="stylesheet" href="//brick.a.ssl.fastly.net/PT+Serif:400,400i,700,700i:f">

It remains to be understood why iOS was already rendering it correctly, or why Google Fonts is misbehaving (?)...