Hi Duolingo Czech team and also kacenka9,
Firstly, I must say that my friends are Prague Czech speakers although there are some generational issues (they learned Czech from their mother who is from Prague, they visit Prague every summer, their grandparents live in Prague). From them I have certainly learned chléb as the word for bread, although some of them pronounce it with the b more voiced at the end than seems normal to me based on my studies in multiple slavic languages. However, this pattern of masculine inanimate declension is either new or irregular. There is a shortening of the stem vowel as well as the irregularity in ending.
I will consult my Prague friends and edit this comment if necessary. But based on Wikislovnik and its English counterpart Wiktionary, it seems that chléb is rather irregular.
I would appreciate the opinion here of an expert in Czech grammar if such there be out here.
I am not an expert grammarian but if your friends' mom comes from Prague, it totally could be a generational issue. Czech evolved a lot in last 50 years, not always in a good way. The written proper Czech and spoken are in some regions like two different languages. My grandmother would write and say chléb. My parents might write chléb, but say chleba. I would write and say chleba only.
Why is the singular genitive of "chleb" "chleba"? I thought the -a ending was only for masculine animate nouns, and the usual ending for masculine inanimate was -u (stolu, hradu).
The problem is elsewhere. We have two words for bread CHLÉB and CHLEBA. Chléb sounds super proper and it might be used in Moravia but good luck coming across it in Prague. Even if you do, it is rarely used in other than nominative case. Not sure why. I actually had to look up, how to decline it, because I never had and it sounded weird in my head. So we tend to use CHLEBA for all other cases.
That said we probably should edit it, though we would teach something that would place you, as a speaker, several centuries away from your listeners.
One more comment: I am unable to determine from this forum who works for duolingo and who doesn't.
I don't know that that's necessarily problematic. That is in fact the beauty of the concept of wiki. However, I am always left with a certain curiosity as to whether my questions have been answered by someone related to the team that posed the original issue.
Nobody who contributes to any of the courses and discussion boards works for Duolingo. Duolingo employees provide technical platform and some administrative support to volunteers who create, edit and discuss the courses.