'Strengthen' does not do weak words
I was looking through my word list, when I found that the word strength of two or three words (phrases, actually) was very low. So then, I decided to use my main 'strengthen skills' button. But surprisingly none of those words came up. I thought I'd give it one more go. Still nothing. Then I thought I'd go to that particular lesson (in this case, Common Phrases), and use the 'Strengthen Common Phrases' button. Even this time it touched none of those weak word; on top of that it only brought up very basic phrases like: non!, bonjour, bienvenue, etc., things that I never get wrong.
I think there is something wrong with the algorithm being used to select words for the Strengthen Skills task. Could you guys take a look under the hood for me and tell me if it is the case that I am missing something or making some mistake?