Word Strength decreases way too fast
I am not sure is only me or a general thing, but lately, the word strength (and thus the "You can read xx% of German") decreases way to fast. I do 20-30points, with some rounds of Words (with the cards), and then a new lesson. And it keeps decreasing over time.
For instance, the word "Saft" (juice in German), which I know way before I began practicing. I practiced it yesterday and it was on "Still strong". Today is already on "Overdue". Like this, many words. (More than half of yesterday words are on "Overdue"). Right now, almost half of my words are already in Overdue.
It is a bit demotivating knowing that, even if I practice old lessons, I can't keep the percentage high :( Am I doing something wrong? Did they changed the "decreasing speed"? Or am I just supposed to practice more each day? [which is a bit boring if it keeps me asking words I perfectly know].
EDIT: some words increased from Overdue to "Time to practice" without me practicing O_o