This is very confusing. If I understand it properly, we can distinguish "the juice glass" (το ποτήρι του χυμού) and "the glass of juice" (το ποτήρι χυμός). We don't say in English, "the juice's glass", although this is what "to ποτήρι του χυμού" indicates, but we translate it as "the juice glass".
Leaving out the preposition in English is the semantic reverse of leaving out the preposition in Greek, which will confuse us. Might we say "the glass for juice"? or is 'του' always and only translated 'of'? I know we can say, "το ποτήρι για το χυμός", but it seems a too rigid adherence to 'του' = 'of' is part of the problem people are having with this, partly because in English, 'of' is used in a variety of ways.
"Of" also indicates "material made of". There is no confusion with juice, because we don't make objects with juice, but in other cases this can add to the confusion. So we have at a minimum possession, purpose, and material potentially indicated by 'of'. According to the help notes for this module, the genitive case only indicates possession, so the emphasis on 'of' is, I think, misleading and the notes are oversimplified.
Yes, we refer to the glass used for juice as "the juice glass" I do not find "the juice's glass" anywhere in our incubator. Where did you see that error. Please send a screenshot.
Using irregular collocations such as "the glass for juice" could be included in an alternative translation but it's not fair to show it as the main translation.
In addition, we have as correct translations both: "The juice glass." and "The glass of juice." since in Greek it could mean either.
We will revise the notes as we are preparing a new tree. Thank you for the notification.
Yes, it seems "you got away with it". Sometimes, the program that grades the exercises overlooks something it should reject.
It's good that you recognized the mistake and know what the right translation should be.
You could have Reported this at the bottom of the exercise page as:
-"My answer should not be accepted". that way Duo keeps records and can correct the program.