This issue was spun off of issue #3157 'Merging a change from a path's natural history creates self-referential mergeinfo'. The current mergeinfo inheritance design is simple: A path without explicit mergeinfo inherits the mergeinfo of its nearest parent with explicit mergeinfo, adjusted for the path difference between the two. E.g. /branches/b1@100 has mergeinfo of '/trunk:50-73' /branches/b1/src/README@100 has no explicit mergeinfo, so it inherits '/trunk/src/README:50-73' (yes, we assume b1/src has no explicit mergeinfo either) This is fast and works fine in most cases, but when a merge is recording mergeinfo describing a merge on a path that has no explicit mergeinfo, it combines the path's inherited mergeinfo with the new mergeinfo describing the merge. In this way, inherited mergeinfo is made explicit. A minor problem with this is that the inherited mergeinfo might be describe a merge source that doesn't exist. For example: A) Assume an unremarkable (i.e. trunk, tags, branches setup) repository with no mergeinfo B) Copy /trunk@100 to /branches/b1 in r101 C) In r102-300 assume various changes are made to both trunk and b1, including: In r152 a new path is added /trunk/src/NEW-README In r275 a change is made to /trunk/src/NEW-README D) In r301 Merge ^/trunk branches/b1 -r100:200 This results in the mergeinfo '/trunk:101-200' on branches/b1 E) Now merge ^/trunk/src/NEW-README branches/b1/src/NEW-README -c275 In step 'E' the target has no mergeinfo of its own, but inherits some from the root of the branch. When the merge records mergeinfo describing the merge it adds this inherited mergeinfo ('/trunk/src/NEW-README:101-200') to the mergeinfo describing the merge ('/trunk/src/NEW-README:275') and records it on the target. This results in the mergeinfo '/trunk/src/NEW-README:101-200,275' on branches/b1/src/NEW-README. There are two problem here, if we break the mergeinfo into three parts we see that only part of it is legitimate: 1) '/trunk/src/NEW-README:101-151' This merge source doesn't exist! 2) '/trunk/src/NEW-README:152' This merge source is self-referential! 3) '/trunk/src/NEW-README:152-200,275' This is legitimate. This issue tracks the problem of nonexistent merge sources, the problem of self-referential mergeinfo tracked in issue #3668.