Hi,
I posted an issue on the php client project page and wanted to make
sure it was seen.
In that lib when you don't give an expiration it will remove the
cache. in my case what i needed was the access token.
I don't know what it does in the other client versions.
i also posted the fix with it.
http://code.google.com/p/opensocial-php-client/issues/detail?id=67