There is a bug in the shipped Safari 9 that results in strange characters being rendered when both ligatures and soft hyphens appear on the same line. (The bug is only triggered when the font actually supports ligatures, e.g. with Open Sans.)
Fortunately, adding the following line to your CSS fixes the font rendering and preserves ligatures:
-webkit-font-feature-settings: "liga"; font-feature-settings: "liga";
If you enable
Add workaround for Safari hyphenation bug, this CSS property is inserted into your page automatically.