Unless exchanges explain that they will gurantee our split security, we can't trust them and I also don't know what to do in this position. Nobody is clear so far including exchanges.
Even if exchanges do promise you that you will get what belongs to you, you shouldn't take that for granted. After all, exchanges may change from standpoint at the time something is happening that they haven't seen coming. If you proceed to leave your coins there anyway, despite all the warnings and statements from the exchanges themselves, you should not complain when things don't play out as you might have expected. Either way, your Bitcoins will remain safe, you just risk losing the potentially free candy.
In my situation, I am a trader, which will basically mean that I leave an x number of coins on-exchange in order to do some trading. I fully accept that I may not end up getting the free candy (the alt) in case of a chain split. Other than that, I will make sure that I have less coins than usual on-exchange (likely in the range of 50% of what I normally would trade with).