The strengthen skills now strengthens skills
For awhile it seemed like strengthen skills just reviewed what ever words where "oldest". Meaning the words you probably knew very well but hadn't practiced in a long time. The ones from the top of your tree.
Now it seems that strengthen skills actually has you strengthening your weakest words.
Hasn't it always done this? I am not sure but for me it always seemed to do this as soon as all already learned skills are golden.