IE has two known issues with CSS parsing.
- Internet Explorer will only load the first 31 stylesheets and will ignore the rest.
- IE versions 6, 7, 8 & 9 all have a limit on the number of selectors allowed in a single CSS file. Its 4095 selectors in a single CSS file. Once the limit is reached, IE silently fails and just ignores any further CSS in the file leaving parts of your site totally unstyled.
So, what to do in those cases? For the first issue, try merging all the CSS files into one or atleast try minimizing the number below 32. And for the second issue try splitting the huge CSS file into two to make it tolerable for IE.
For more information:
Happy CSS coding! And DIE IE, DIE! :)