This sort of thing is driving me nuts. I am frequently marked incorrect for expressing a translation in slightly different words. I don't know if it is because this course is new, or if this is an issue elsewhere in Duolingo. But right now it is discouraging me from continuing to use the program.
I have felt the same way, but perhaps this challenges us to think, to focus on nuances. Chomsky always heralded native speaker intuition as where a language is at. Surely those putting this course together are doing their utmost, which IS impressive if you look at the competition.