the suite.maybeSubSteps function loops over all substeps and invoked them one by one:

On line 352 new ctx and err variables are created in the scope of the if statement that shadow the ctx from the argument list. As soon as the if scope completes ctx becomes the original context that was passed in to the function again. The effect of this is that the context returned by the subset is discarded.

This can easily be tested by modifying the standard example to add a multistep:

func InitializeScenario(sc *godog.ScenarioContext) {
	sc.StepContext().Before(transformStep)
	sc.Step(`^I eat (\d+)$`, iEat)
	sc.Step(`^there should be (\d+) remaining$`, thereShouldBeRemaining)
	sc.Step(`^I eat (\d+) godogs out of (\d+)`, func(ctx context.Context, a, b int) (context.Context, godog.Steps) {
		return ctx, godog.Steps{
			fmt.Sprintf("there are %d godogs", b),
			fmt.Sprintf("I eat %d", a),
		}
	})
}

with a matching scenario:

    Scenario: Basic multistep
        Given I eat 8 godogs out of 14
        Then there should be 6 remaining