OK, so I need to identify a weird bug somewhere in the Excel CSV Reader! <sigh> If you were loading to PHPExcel while the file was still in PHP's temporary upload directory before being moved, then I could understand this.
I can't reproduce it: it loads cleanly for me using both the 1.7.7 and 1.7.8 code. Can you try using
$reader = PHPExcel_IOFactory::identify($filename);
and then echoing the value of $reader just to confirm.