Re-tested component-showcase with icefaces-compat.jar containing the minified JS resources but I could not reproduce the problem described above. The JS resources are loaded and evaluated without any issues.
The problem described by http://jira.icefaces.org/secure/attachment/12965/screenshot-01.png is obviously caused by the failure to load compat.js and icefaces-compat.js resources. The cause of the problem must be on the server since the HTTP 404 errors are sent from there.
Added missing YUI compressor (v2.4.2) library into 'lib' directory. This way 'core' and 'compat' builds can use it to compress the JS resources.