By default, BTC and LTC segwit addresses both begin with 3

Before segwit, LTC addresses always began with an L and BTC addresses began with a 1, which prevented users from accidentally mixing up bitcoin and litecoin addresses. With segwit, they both use a common prefix of 3 by default, and the addresses are "compatible" in the sense that you can accidentally send bitcoin to a litecoin segwit address and vice-versa.

Several users sent Litecoin to a Bitcoin deposit address at BlockTrades

We've had a couple users make this mistake: they got a bitcoin deposit address from https://blocktrades.us, then they sent litecoin to that address from their litecoin wallet or exchange. Unfortunately, the wallets and exchanges can't tell that the litecoin is being sent to our bitcoin wallet that won't see the litecoin transaction. This means we get no notifications that anything has gone wrong until the user contacts us and asks us about his litecoin transaction.

We've been manually handling such mistakes, but it's very time-consuming for everyone concerned because it requires keys to be moved between wallets, so please if you're sending bitcoin or litecoin, double check that you have the correct address type.

Potential issue when specifying your receive address too

When you input a receive address into BlockTrades, it's important to make sure it is of the correct type also. So if you want to receive Litecoin be sure you get a litecoin deposit address from your exchange or wallet, and make sure the Send type is Litecoin on our site. All obvious instructions I'm sure, but doesn't hurt to double check before you transact.