[Mediawiki-l] Domain name changes to dot-quad IP address

[rex]

http://www.mywhatever.org/mywiki changes to http://64.xxx.xxx.xxx/mywiki
in the browser. Also, email notifications have the the IP address
instead of the domain name. This is probably due to some config change I
made, but I can't find it.

It doesn't happen on pages that are not generated by Mediawiki, so I'm
fairly certain it doesn't have anything to do with Apache.

A pointer to the small change needed would be appreciated.

Thanks,

-rex