[short summary is at the bottom]
Lada and I are merging the DBus feature branch now and got this puzzling error message from svn merge --reintegrate: svn: Cannot reintegrate from 'http:...' yet: Some revisions have been merged under it that have not been merged into the reintegration target; merge them first, then retry.
It is because the property is supposed to be set only on the branch root (http://svn.opensuse.org/svn/yast/branches/tmp/lslezak/core) but it was present also on various files within the tree, with 6 different values, so svn thought that we have a sophisticated merging set up and required manual intervention.
It turns out that all of the svn:mergeinfo in the subtree were unnecessary. Svn just creates them whenever you rename a file. The reasons are so obscure that even this article which helped us understand the problem does not mention them :-(( http://blogs.open.collab.net/svn/2008/07/subversion-merg.html
Short summary =============
If you do svn mv OLD NEW Then also do svn propdel svn:mergeinfo NEW # svn pd ...