Bitcoin transactions are reversible! Once a transaction goes out of the wallet, it's done! There's no way to reverse it back to the same wallet without creating a new transaction for it! That's what exactly happened in your case. The transaction of 0.1 btc wasn't reversed, rather transferred to a new/same address.

Your case sounds real absurd! You mentioned you have blockchain wallet, is it the core bitcoin wallet or the online blockchain wallet? Most probably your account is hacked and accessed outside your knowledge! Wallets doesn't have brain. They don't send transactions unless they are instructed to do so!