Im having the same problem with HSK level 4. I can water three or four and then in the multiple choice questions, there's nothing showing up to click. Also, the English and Chinese is mixed and I'm having to answer in chinese 汉子, which despite it being good practice, It's not right.
Yes, Mandarin is broken. It explains why in that thread over on the Mandarin forum. By all means complain if you think it shouldn't be broken, or if you'd like a bit more notice of maintenance, but here, in this forum, are lots of posts saying it's broken, each with a link to the explanation. There is really no need for more posts saying it's broken, and exactly how it's broken.
I do not think that this is the same bug. In the thread you linked to, it states that the system does sometimes not accept the answer, or that it wants the Pinyin answer when it states that it wants the English answer, or something in this fashion. However, ITT we complain about no answers being eligible at all.
BTW, I do really think that there should be some kind of announcement on the website when it goes into maintenance and things are going to be broken. This would also prevent spam in the forums.