decay rate never improves
It seems that no matter how many times I get a word right its decay rate does not improve. I have experimented with one word "manteau" making sure I pratice it and get it right once a day, yet it still decays at the same rate (it goes down to two in less than 24 hours). I can't say if this affects all my words, but it affect a lot of them. It is getting to the point that "practice weakest words" is useless, because it only brings up words I in fact know very well, because I have practices them daily for weeks.
Is this something that is only happening to me, or is it a general problem?
I have similar suspicions. I also notice that I seem to have very different decay rates between languages. My Italian seems to decay incredibly fast, and I find myself being given sentences every week that I have seen many times and (I think) never got wrong - the one about 'if you have a cake, why don't you eat the cake' comes to mind - whereas Spanish barely seems to move. German and French come in between.