Some recent versions added /etc/portage/bin/post-sync to run commands after syncing the tree. emerge-delta-webrsync should make use of this too.
Created attachment 99680 [details, diff] post_sync.patch add hook for /etc/portage/bin/post_sync and change to "emerge --metadata"
Created attachment 99681 [details, diff] post_sync.patch without --metadata change
Created attachment 99682 [details, diff] post_sync.patch moving post_sync after "emerge --metadata" like Betelgeuse suggested. sorry for the bugspam.
Committed a patch in 3.5.1-r2.