set operator '-' not working with set() function?

Here is my working code for this challenge. For some reason line 7 is not actually creating a set 'others' that has 'word' removed. Yet the seemingly equivalent line 8 that is commented out works just fine. What is going on here?

def checkio(words):
    print('words: {}'.format(words))

    for word in words:
        print('checking {}'.format(word))
        length = len(word)
        others = words - set(word)
        #others = words - {word}
        print('others: {}'.format(others))
        others = set(x for x in others if word in x)
        if any(word == x[-length:] for x in others):
            print('returning True for {}'.format(word))
            return True

    return False