This happened to me some months ago too. Now that BTC is climbing so fast it especially hurts that they don't have a system in place to prevent things like that from happening. In my case i was using electron cash to send my BCC to bittrex and sell it. I tried that like a lot of times and wasn't working. Some days later i wanted to try again but instead opened the original electrum client (which looks exactly the same...) and send my BTC to the BCC bittrex address...

The thing that upsets me the most is why do they use different addresses for a forked chain? This would not happen on a real wallet as i would have the private keys for both chains. Also it is that difficult to program an script that credit BTC back to the bittrex BTC address for every BCC owner that has some balance (lets say 50$) on its BTC address? They could pay the transaction fee from the balance, and even take a fee for the service if they want to. A company that cares for their customers should not let this happen.