Add a regression test for #656

[airbreather]

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Resolves #656

I came here to fix that linked issue, but it turns out that the issue no longer reproduces on the latest version.

Digging around, I can confirm that commit e1986a459599772699a9cdaa712193da5db6de55 was the one that fixed it. I can't quite tell why that would be, but this exact automated test definitely passes at that version and definitely fails immediately before. :shrug:

Regardless, before I call it "good enough", I would appreciate it if you could add this automated test to the repository as a safeguard, especially since I can't tell why that commit "ought" to have fixed this.