This should be Exhibit A in the case against Duolingo's handling of contractions.
Their contraction algorithm is not very smart because it cannot handle the conversion DO YOU NOT <> DON'T YOU (and in general any contractions where intervening words exist). If we include the contracted DON'T YOU in the answers, the system automatically accepts the non-existent expanded form DO NOT YOU.
Clearly that limitation produces highly undesirable results even in people with level 25 in English. I suggest it is not their fault. And nothing we can do about it. No matter how many discussions we put this in, the wrong habit is reinforced countless times every single day. I can only hope that @jenda48 will now be free of this particular problem.
It is unnatural in English to start a question with a negative contraction and remain neutral in tone.
"Don't you have any other magazines" in English has a tone of anger, disappointment and surprise. It could also be quite rude.
'Do you not have any other magazines' is slightly less combative, but still not a neutral question in English.
Negative questions in English are uncommon as they usually express something other than just a question.
Most native speakers would ask 'Do you have any other magazines?' as a polite, neutral request for information.
In Czech, the same tone of anger, disappointment or surprise is expressed by the word order "Jiné časopisy nemáte?" where the negative verb is placed in the stressed position at the end.
A neutral question would start with the verb: "Nemáte jiné časopisy?" which would then have to be translated as "Do you have other magazines?" And of course, "Máte jiné časopisy?" is also possible and the difference between the positive and negative question (while keeping the verb first) is a subtle nuance in Czech.