As mentioned in item #1 in http://subversion.tigris.org/issues/show_bug.cgi?id=3669#desc7, a subtree merge within an uncommitted working merge can create mergeinfo on the subtree target that describes invalid path-revisions. The recipe is this (assume a uniform-revision target WC): 1) Merge -rX:Y from ^/SRC to target-WC such that working mergeinfo is recorded on target-WC describing the merge. 2) Before committing the merge in step 1 do a subtree merge under it from ^/SRC/subtree to target-WC/subtree, where the latter has *no* explicit mergeinfo prior to this second merge. In addition to whatever mergeinfo we record to describe the merge, target-WC/subtree will first inherit '/SRC:X-Y'. Great, *except* if ^/SRC/subtree didn't exist until some revision Z, where X < Z, then the mergeinfo '/SRC/subtree:X-(Z-1)' describes invalid path-revs (or '/SRC/subtree:X-Y)' if Z > Y). Test incoming for this in a moment.