Cookie issue ($Version)

A site I'm working on in PHP is having some issues with cookies with the Kindle web browser.

I'm printing out the cookies using print_r($_COOKIE) and in Firefox everything looks fine (and it works fine). However on the Kindle the cookie appears slightly different.

It has a named array index "[$Version] => 0". Also all my cookie values have the following attached to the end of them; ", $Version=0". So when I go to retrieve them they aren't what I expect them to be. I imagine this is the issue with the site. It's fairly trivial to remove the ", $Version=0" off but I'm curious if anybody knows why it might be putting it there? If it's a side effect of the $Version index I'd rather just figure out a way for that to stop happening.

I guess it could be user agent related (it's not my code) but I did grep for Version=0 and didn't get any results. It does look like the code is using YUI from Yahoo.

This RFC also seems to mention something about Version... http://www.ietf.org/rfc/rfc2109.txt

I'm not well versed in web stuff but thought maybe some of you might have encountered this or at least know why the browser might be doing this.

Edit: I just spoofed the user agent in Safari to the Kindles and it works the same as Firefox... So probably nothing to do with the user-agent.