I would use the gulp-bless plugin to separate bower CSS files, because the generated minified file is too long and isn't processed completely in IE 9.
But the file generated by gulp-bless plugin isn't replaced in the "index.html" file by gulp-useref plugin.
The gulp useref plugin also can't join all files, would keep the structure generated by the gulp-bless plugin.
File "index.html" (css imports and useref)
File "gulpfile.js" (part of build task)
Someone has any idea?
Solved by removing the sourceMap.