Once again IE tries to trip us up.
How you ask?
IE versions 6, 7, 8 & 9 all have a limit on the number of selectors allowed 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.
File size, number of lines or amount of whitespace are irrelevant. Minifying CSS will not help you here.
Note: BLESS is built into CodeKit.