Sorry, actually is a newer version of behave, I've run this against master(f68e7e4).

FTR here[0] is where they changed `undefined` by `undefined_steps`

[0] - https://github.com/behave/behave/commit/f68e7e40d1e971f8bb178530251b0e8a88de3107#diff-6b74cab5955bbc0f7bce44cca7cfd975R373