Backports opened against wrong parent PR

[JoeSzymanskiFAN]

I've run into a strange scenario every once in a while that I haven't been able to track down.

Rarely, we will have the backport script run and one backport PRs that have the correct commits, but are associated with the wrong parent PR.

For example, PR 1234 will merge, which kicks off the script. It runs with a command similar to:

backport --repo "repo" \
                --accessToken "${GITHUB_TOKEN}" \
                --pullNumber 1234 \
                --noFork \
                --nonInteractive \
                --commitConflicts \
                --label "automated backport" \
                --source-branch "sourceBranch" \
                --target-branch "targetBranch"

the output of the backport job correctly lists the commits from PR 1234, but incorrectly lists the source PR as something different, say 2345 (which is a still-open PR).

Any debugging suggestions would be helpful. I haven't been able to track down why this mismatch is occurring, and it's been causing some confusion when it happens.