Exchanges & POS coins

I am not sure where to ask this question and it seems not many have any info on it.

My question is about exchanges and POS coins. Do exchanges stake on there main wallet for POS coins? And if they do is there some hidden rule as to how the exchange dumps its staked coins? I have been curious about this for a while. More people leave there coins on exchanges now days. This opens up an exchange to be able to mass gigantic amounts of POS coins and stake the shit out of them and then dump them onto the unsuspecting market.

I am almost thinking that a flag for if the coin is on a known exchangeshould be set turning off staking for coins that are at known exchange wallet addresses. (if possible, would have to think so since the full capability of the blockchain is still yet to be discovered)..

There are so many new high POS coins out now and people tend to forget that each of those coins when on an exchange sits in a main wallet in mass and if the exchanges stake it reduces the overall value of the coin because when it come down to it an exchange does not care about dumping its stake.

Anyways anyone have any info on this? or is it just as we probably all think, exchange stakes the crap out of coins and those are the random mega low dumps that occasionally happen with pos coins (happens with all coins but pos coins seem to have nice hefty dumps often. of course free coins = free btc so...)