Index resulting from repo.merge_commits() is owned by the repo, unsavable

Given a merge index with conflicts, when trying to save it to the current index the operation fails with a runtime error:
"the given object is already owned by another repository (RuntimeError)"

The use case here is to implement a workflow similar to git-merge. We try to perform a merge and if it fails we write the result of the merge into the current index and pass control back to the user to resolve conflicts. This fails and merge_index is essentially impossible to write to disk (until the conflicts are resolved).

require 'rugged'
repo = Rugged::Repository.new("/source/test")
merge_index = repo.merge_commits(repo.branches['child'].target, repo.branches['master'].target)
if (merge_index.conflicts?)
   repo.index = merge_index  #fails 
   merge_index.write()
end

Reproduce the conflict case through repo.merge_commits(...), then inspect the ownership path used by repo.index= and merge_index.write(). Confirm the fix by verifying that a conflicted merge index can be assigned to the repository's current index and written to disk without the ownership RuntimeError.