This was so hard to believe I just had to blog it. Quoting from the Microsoft KB for the bug:
• All style tags after the first 31 style tags are not applied.
• All style rules after the first 4,095 rules are not applied.
• On pages that uses the @import rule to continously import external style sheets that import other style sheets, style sheets that are more than three levels deep are ignored.
Affects IE versions 6-9. Lovely. Here’s the source: http://support.microsoft.com/kb/262161