Is there a reason Git ReReRe might not succeed?

Question

I have an integration branch that I use to test multiple features at once. Sometimes the features conflict with each other, and Git ReReRe has been invaluable in helping to avoid re-doing the resolution.

But this time, I have a file for which I have a resolution in rr-cache, Git uses the resolution, but then complains I have to resolve the conflict myself.

Simple merge did not work, trying automatic merge.
Auto-merging src/file1.xxx
ERROR: content conflict in src/file1.xxx
Auto-merging src/file2.xxx
Auto-merging src/file3.xxx
fatal: merge program failed
Resolved 'src/file1.xxx' using previous resolution.
Automatic merge failed; fix conflicts and then commit the result.

$ git status
On branch integration
You have unmerged paths.
  (fix conflicts and run "git commit")
  (use "git merge --abort" to abort the merge)

Changes to be committed:
    (...more files...)
    modified:   src/file2.xxx
    modified:   src/file3.xxx

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   src/file1.xxx

I've tried git rerere forget src/file1.xxx and letting it recreate the ReReRe resolution. I've even tried setting the postimage by hand. But nothing seems to convince Git that the postimage should be applied and accepted.

It's not a difficult conflict, but I'd really like it to happen seamlessly.