Internet Explorer background image not showing

Hello!

Before you say: "Hey I recognize that!"
- The theme I built is a combination of WordPress.com (tables), PlayStation.com (menu), WPMUdev.org (old (thread nesting) and new (header title) ) and StudioPress.com (layering) and some more. I had to get inspiration from somewhere :')

Anyway, let's continue:

In Internet Explorer (11) my background image isn't showing on the front page.
All styles and images are being pulled from a CDN and it seems to be working brilliantly if the image isn't too big.

I'm not exactly sure what the sweet spot is but this is definitely a factor.

The background always gets loaded by the browser, it's just not visible, until/unless:
- The browser window resizes.
- A non-inline CSS style in the Dev Tools (F12) gets added/activated/deactivated.
- When "Always refresh from the server" is activated in Dev Tools.

I said non-inline because I also tried jQuery CSS with and without a timeout.

https://lightspring.hostmijnpagina.nl/ = Not working
https://lightspring.hostmijnpagina.nl/2014/12/28/hallo-wereld/ = working (repeating small image behind the title).

If you dig deeper you can see that the post page has its image through CSS in the header using <style> attributes. The reason for this is because a featured-image would show if present. This however doesn't solve the problem (I tried).

Quite weird, I've faced this problem many times before, but now I want a 100% optimized website that doesn't load junk like backstretch.

FYI WordPress.com also has this problem lol.
Modernizr doesn't help either.

Any idea's? :slight_smile:

P.S. the font for writing a new post is so cheerful here, I like it! ^^