Suggestion: have "Strengthen skills" work with bonus lessons

[DocOx]

I have a few bonus lessons in my tree and some of them have lost their gold status. I was therefore hoping that by "strengthen[ing] [my] skills", I would be able to get them back to gold status, but it would seem that "Strengthen skills" doesn't work with bonus lessons? If that's really the case, it would be nice if "Strengthen skills" was to take them into account. I like my tree to be gold... :)