> Does that make sense? Shouldn't it say "FIXED"?

It should.  Your spec is pretty irregular; from within a spec you are creating an example group (and a nested spec) and running it.  As a result `RSpec.current_example` gets cleared when the locally created spec completes (but before your "supports 'its' with an implicit subject" spec completes) and the error occurs.

In rspec-core, we have special sand-boxing logic that allows us to create on-the-fly specs and run them like this:

https://github.com/rspec/rspec-core/blob/869d2e5eb9e932daa3c7d77c52354826bd37baa2/spec/spec_helper.rb#L54-L87

You lack that here, so it had this problem.

I just pushed a PR (rspec/rspec-core#1090) that should fix this, though.

> Second, is it right that the API call to extend shouldn't be sufficient (i.e. shouldn't it be doing this include as part of that implementation)?

`RSpec::Core::Configuration#extend` causes the module to be extended onto each example group.  `RSpec::SharedContext` is not an example group so there's no reason it would be included there.  You have to include it yourself to make it available.