There are 2 settings...

Preferred content culture and Preferred user interface culture. Both have the value "Default" when a new user is created.

If I explicitly set the Preferred user interface culture to English (in my case). The problem appears to go away.

To me the question is why does the setting of "Default" produce a zero for the cookie value. This happens is more than one Kentico instance that I maintain. Also, it seems to be only IE that has the issue.

Thanks!