I'm glad you asked about this.  It felt like a hack and I have no idea what's going on that causes this branch to get hit..but I have a test that fails w/o it.  The test case that requires this is here:

https://github.com/vcr/vcr/blob/acc66dcd01b8fba48c2fd6dcfeb7cdd5fb3955be/spec/support/shared_example_groups/excon.rb#L21

It's using a response_block to stream and also uses the `:expects` option but is getting back a [404 instead of a 200](https://github.com/vcr/vcr/blob/acc66dcd01b8fba48c2fd6dcfeb7cdd5fb3955be/spec/support/sinatra_app.rb#L49-L52).

The easiest way to repro this if you want to troubleshoot it is to clone VCR, bundle install, change this line to `if false` (so the branch is never taken) and then run:

```
$ rspec spec/vcr/library_hooks/excon_spec.rb -e "unexpected status"
```

...and it'll run the one spec that fails without this branch.

As you say, it would be great to understand why this is needed and/or change Excon so it's not.