-object.xml files are loaded without any order rule. This makes mangement of portal/page definitions very difficult with "overwrite" mode since you can't assume if parent has already been loaded or not.
It should be easy to fix this (I've made a temporary patch) : descriptors URL are already sorted before parsing, but their parsing results are put in a non-sorted Map (cf. org.jboss.portal.server.deployment.jboss.PortalDeploymentInfoContext).
PS : my -object.xml files follow this structure (all with 'overwrite' mode) :
toppage-x-object.xml (with all its subpages)
toppage-y-object.xml (with all its subpages)
toppage-z-object.xml (with all its subpages)