Chrome inconsistency when rendering Google Fonts

Question

These screenshots are both taken from the same source code:

You can probably guess it, these are rendered with the latest Google Chrome (43) on Linux. As you can see, the result varies greatly, and I have no idea why.

The only thing I did was open the page in a new tab, and somehow I get on of those results randomly (usually one of the first 2 screenshots)

The relevant parts of the code, i.e. everything that touches the font -family, -style or -weight:

@import url(https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,600);

body {
  font-family: 'Open Sans', sans-serif;
  font-size: 16px;
  font-style: normal;
  font-weight: 300;
}

h1, h2, h3 {
  font-weight: 600;
}

.timetable .organisation {
  font-style: italic;
}

.timetable .title {
  font-weight: 600;
}

You can see it for yourself there (the code is live, I don't care about that bug enough to make a dev copy)

As far as I can tell, the first screenshot show the correct font rendering (where it's thinner), the other one being sans-serif, which is next in the font-family list.

Google Fonts seems to be serving the font in WOFF2 format (checked by opening the imported CSS directly in a tab). I have no idea how to check the font format actually loaded in the page.

I have tried everything remotely related:

• changing the order of the CSS and JS inclusion
• adding an opacity animation (even though that bug should be fixed)
• adding some font-smoothing

This "related questions" are not related:

• Chrome not respecting font weight? → The font-weight does exist in this font.
• Inconsistent font size rendering issue on Chrome → The font-size is set in px.
• Chrome is not displaying google fonts when all other browsers do → The font-style is correct.
• Chrome not loading website when Google Fonts are installed/running → The page doesn't freeze.
• Google I/O - Roboto Font (new version) font rendering issues in Chrome (windows) → I'm not on Windows.
• Google Chrome Font Rendering → I'm not on Mac OS.
• Chrome on Mac rendering font sizes inconsistently → I don't have any accessibility settings set and my "minimum font size" is set to 10, i.e. much below the sizes used here.
• Font family automatically changes to “undefined,sans-serif!important” in Chrome → disabling all the extensions changes nothing

It might be related to this unanswered question, although my experience differs, as the results change randomly here.