I often find myself not being able to remember words when speaking in Chinese. I know I have studied it on Hanzi Hero and can answer it correctly when I see the characters but when I need to translate from English to Chinese when speaking as a low intermediate the words seem to evade me.
One reason I think is that we never do it this way round on HH. We never get the English word and have to give the pinyin (which could then also practice typing Chinese using pinyin).