If you sync your tree with some RSYNC_EXCLUDEFROM in effect, and then remove the restriction and rsync again, the sync gets canceled as your timestamps are already up to date. The only way I found to fix this is to remove
/usr/portage/metadata/timestamp.chk and /var/cache/edb/dep/timestamp.chk
The best solution would be to include all RSYNC_EXLUDE settings that are in effect into the timestamp files, so that any change in those settings would be detected and the download would proceed anyway.
As a probably easier alternative, a --force switch passed to emerge, to rsync no matter what, would help as well.
Current situation where I experienced this: When switching from the current java axxo-overlay which used RSYNC_EXCLUDEFROM to avoid conflicts with newer ebuilds in the main portage tree.
not worth the effort imo