I agree with the fact that author has to at least mention the fact that you need to work around this special case. Right now the description of the task and the expected results are different. Which is not a problem to work around, but it's not right.

Oh, I don't really know that I had to close the issue, sorry. But anyway, I think there is no idiots on this site and when they see an error they could easily fix the problem in their code and pass all the tests and it's much easier than to make a note about it (that's a low chance, but who knows? ;) ).

I fixed problems in my code and passed all tests but still can't understand the task. So please, just explain me why two similar chars like 'kk' after the sorting have to become 'k'.

P.S. Should I open an issue next time if I have a similar problem or just post the comment?

No issue.
Do not create an issue, if you are not sure, what is the problem.
798 people solved this kata without problems, so I really think, the problem is in your code.

And next time you should close the issue yourself, when you solved the kata!

Got this error: 'hzyxusecbm lfbah ayusifcae uumlbi hh crhby' should equal 'hzyxusecbm lfbah ayusifcae uumlbi h crhby'
I don't really understand why 'hh' becomes just 'h'. As I understood I have to sort chars in every word except first and last char. Change description on that task, because in every word with two same char you have to delete one from the word. For example 'kk' -> 'k'.