Canon Speedlite 580EX II: White balance?

[photogreenls]

Here is fresh review on Canon 580EX Mark II:
http://photo.greenlightstreet.com/www/inde...frmArticleID/6/

It says: "...automatic white balance works better with external metering on some cameras (for instance, Canon Digital Rebel)...".
Can anybody comment on that? Is this due to some cameras not being able to read white balance information coming from the flash? Thanks!