Stefan Fuhrmann reported:
There is yet another problem with sub-tree mergeinfo:
(1) User A performs a sub-tree merge causing the mi property
to be added to the sub-node. No commit, yet.
(2) User B commits a merge at the branch root, modifying its m/i.
(3) User A updates and commits their merge.
Now, the sub-tree mergeinfo does not reflect the changes
made to the root node m/i. If the latter are operative on that
sub-tree, the data is inconsistent and can create conflicts.
See the dev@ email thread "'svn up' may cause inconsistent mergeinfo" started on
2014-12-11, archived at e.g. <http://svn.haxx.se/dev/archive-2014-12/0065.shtml>