Words and characters that do not appear on HSK lists I have just posted a question about HSK characters list not matching the most common characters list, but I think this question here is a bit different.

I also wonder why do HSK tests have so many words on them that do not appear on any of the level lists (like a 呗 that I saw on an HSK 5 and it's not even at the level 6 list) or words that do appear in a given level, but are advanced compared to the level they appear (like a 公共汽车 appearing on level 1 even if it's only a level 2 word).

Questions:
1. Why don't the people that prepare the exams follow their own lists?
2. How should a student study for HSK with such a chaotic list situation?

Thanks!
Well...firstly thank you for loving (or pretending to love) Chinese language.
I know quite a lot of examples that the students passed HSK Level 6 but still have a terrible level of conversation. Yes. As a commentator said, HSK doesn't include oral test. Further more, its scope doesn't necessarily match the scope of the most commonly used Chinese vocabulary. Therefore, a word list for a particular test is restricted to this test only.
Also, it's a bad idea to look for a frequency table in order to figure out what should you learn. Think about how you learn your mother tongue. Is the most frequent word learned first? Come on, ignore that frequency list.
Finally, If passing HSK is your top priority, use HSK's vocabulary. It limits the scope of words and expressions you need to pass it.
One last comment: Don't forget to talk and learn more from the Chinese people themselves. They are the real ones that master the language.