Bitstamp screwed up a while back and lost $5 million in a social engineering attack. I don't know if they've done any type of proof of solvency post-attack, but their exchange behavior lately has been very strange. Someone has been really desperate to try and keep prices low there. For example, right now prices are $454 on Finex, BTCE, and Coinbase, yet in the following picture, you can see someone has a wall up at $452 trying to prevent it from going higher while also dumping coins into the buy side. They are essentially just setting money on fire doing this in an attempt to stop Bitcoin from rising.
It's possible it's just some rich entity that really doesn't want the price of BTC to go up because they want to accumulate as many coins as possible before halving, but the other possibility is the exchange itself trying to keep prices lower to buy back coins they don't actually have. This is not an actual Gox situation or anything since the coins that were stolen from Bitstamp have been sold off long ago, so it's only an issue if they turn out to be selling you non-existent coins for fiat and you try to withdraw from there.
Here's the link from the July 1st, 2015 robbery:
http://www.coindesk.com/unconfirmed-report-5-million-bitstamp-bitcoin-exchange/It's always possible it's just a manipulator unaffiliated with the exchange, or the people pumping Ethereum trying to stop Bitcoin from rising to prevent their pump and dump altcoin from imploding.
