Merge doesn't happen when "squash commits" is selected

Summary

I hit “merge” on this one quite a few times… yet it never merged. Then, when I unclicked squash commits it merged, no problem. Known bug? gitlab-com/www-gitlab-com!4983 (merged)

Steps to reproduce

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What is the current bug behavior?

(What actually happens)

What is the expected correct behavior?

(What you should see instead)

Relevant logs and/or screenshots

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Output of checks

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Results of GitLab environment info

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(For installations from source run and paste the output of: sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production)

Results of GitLab application Check

(For installations with omnibus-gitlab package run and paste the output of: sudo gitlab-rake gitlab:check SANITIZE=true)

(For installations from source run and paste the output of: sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)

(we will only investigate if the tests are passing)

Possible fixes

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