I think the code is in the CSSCompression_Individuals class is causing the issue.
http://drupal.org/node/1324944
url(/sites/default/files/fontyourface/fontsquirrel/Days-fontfacekit/Days-webfont.svg#DaysRegular)
Turns into
url(/sites/default/files/fontyourface/fontsquirrel/days-fontfacekit/days-webfont.svg#daysregular)