See https://issues.jboss.org/browse/MODULES-192 This causes a visible performance degradation - slower startup, higher memory consumption, slower class loading (eg. during deployment of applications). Needs an upgrade of JBoss Modules to 1.3.4.Final.
The performance issue was fixed, startup of 6.4.0.DR10 is ~700 ms faster compared to 6.3.0. Also memory consumption is lower.