The eclipse build omits the platform source components. If you look in /usr/lib/eclipse/plugins/org.eclipse.platform.source_2.1.1/, you'll see it is mostly empty. Instead it should have a subdirectory holding a lot of source components. This is a problem because the missing components include XML schema for parts of plugin.xml. Without these, the PDE plugin.xml editor can't properly edit certain extension points. Also, you can observe an unexpected exception and subsequent strange behavior by trying to open the properties view of an extension point in the plugin.xml editor. I believe this is related to this problem.
I'm handling this one.
I've checked in a fix for this. Will verify with next snapshot RPM.
Moving from RHEL/3/Eclipse to Red Hat Developer Suite product.