IE8 did not pass Acid2

Taken from: http://en.wikipedia.org/wiki/Internet_Explorer

As a result, according to Microsoft, an internal debug build of IE8 passes the Acid2 test in IE8 standards mode. However, the version of IE8 that will be released will not pass Acid2 as it will require pages to specifically request to be rendered in IE8 standards mode, and Acid2 does not request this.