Was this question in a word, grammar, or sentence schedule? Kanji vectors can only be enabled/disabled for word schedules; questions for other schedule types will conform to how sentences appear globally based on your account settings and kanji knowledge.
Renshuu only tests you on kanji it thinks you know -- meaning ones you've studied previously in Renshuu, ones it assumes from the language level you gave during account set-up, or have manually marked "I know this". By default, kanji you do not know will appear with furigana over them, and the furigana will disappear after you have learned them, so the way you're describing how 中国人 displayed, 国 and 人 are marked known on your account and 中 is not. If you DON'T know 国 and 人 and have never studied them on Renshuu, then Renshuu overestimated your level during account set-up, and you can reset your kanji knowledge by using the Kanji Index in the menu.
If you HAVE studied 国 and 人 and simply don't want to see kanji in your vocabulary schedules, in your schedule settings disable the "Meaning→Japanese" and "Japanese→Meaning" study vectors. The "Japanese" vectors will test you on the kanji form of a term if you know any of the kanji in it, and will otherwise fall back on asking you about the kana form; disabling the "Japanese" vectors will allow you to enable/disable the kanji and kana vectors individually, so you can set it to only ask you kana questions without switching to kanji questions as you acquire more kanji.
