Not seeing it - wondering if GAE just pucked - it does that some times :-)
Can you try again?
I'm still seeing it. I don't think its a browser error as it happens in Opera, Chrome, FireFox and Konqueror.
Strange thing is the URL that appears after clicking on a4j:ajax is: http://richfaces-showcase.appspot.com/richfaces/component-sample.jsf?demo=&skin=blueSky
see ?demo=&skin=blueSky. The demo parameter has no value assigned to it.
If I manually set the parameter in the URL like ?demo=ajax&skin=blueSky it works well.
When I follow your link I see the same thing, but you are right putting in the ajax fixes it.
I'll ping you on IRC
So I've been looking into this more. It only happens on GAE, and only occationally. It does not seem to be load based. We are going to look into this more, and I'll create jira track it.
I can't get it to happen now at all, so that is a good thing.