Omega theme not rendering correctly when css aggregation is disabled
Can be because it needs polyfills which are only loaded with aggregation turned on. 

Try with a CSS3 standards compliant browser (ie. latest version of Chrome) which would not need the polyfills at all.

Omega 4 comes with these polyfills:


Selectivizr.js
CSS3 Media Queries JS
Respond.js
CSS3 PIE
HTML5 shiv