This isn't unpickable at all, its just remarkably tedious to do so. The fundamental information leak via how far you can turn before getting stuck is still there. You've just added a mechanism that temporarily locks-in the current key-state being tested, forcing an attacker to return to the initial position before inputting the next key-state. Don't get me wrong, that is a good design feature. But what you have made is still very much in pickable via the same old established principles of lockpicking. You have simply forced the standard technique to be more clumsy and error prone to execute, perhaps requiring some unique tool to measure the subtle differences that give the key away.