Libraries in lib of the Plugin Installer Executable JAR are overridden by their client counterparts, take for instance the output of the following:

plugin$ jar -tvf target/jboss-ejb3-plugin-0.1.0-SNAPSHOT-installer.jar |grep lib|grep proxy

57086 Thu Sep 11 17:13:36 GMT-05:00 2008 lib/jboss-ejb3-proxy.jar
13048 Mon Aug 25 00:22:44 GMT-05:00 2008 lib/jboss-ejb3-proxy-clustered.jar
57086 Thu Sep 11 17:13:36 GMT-05:00 2008 lib/jboss-ejb3-proxy-client.jar
13048 Mon Aug 25 00:22:44 GMT-05:00 2008 lib/jboss-ejb3-proxy-clustered-client.jar

...file sizes for proxy.jar and proxy-client.jar are equal. Contents of these confirm that its actually proxy-client that's in the name proxy.jar.

Leads to runtime errors when starting a Plugin'd AS.