The statistics function is pretty buggy, that is why it has been stripped out of the default 2.3 install. One thing you can check is, is there actually a browser info stored in the database? If you have PHPmyadmin login to that, select your data then click the browse icon on the left of the 'PageView' table. Those are the actual records so check that the browser column has information in it.
I recommend using google analytics as it will provide you with alot more information.