Merge bug causes changesets to be applied although this should not be the case

Hello,

in SVN 1.7.9 and earlier versions (als tested 1.7.7 and 1.7.8), it can
happen that a merge succeeds although the patch definitely cannot be
applied. This happens when the changeset to be applied deletes some
lines at the very beginning of a file. Such a changeset is happily
"applied" by "svn merge" although the target file does not contain the
lines to be deleted.

Please see the associated test case. The merge after r4 succeeds
(without having any effects), although the corresponding "patch"
command correctly fails. Basically, "svn merge" allows to apply
files2.patch before files1.patch, which is clearly wrong.

Is this a known bug? Do any workarounds exist to prevent this bug from
occurring?

Regards,

Christoph Schulz