Cognito user pool Unexpected Behaviour

I had an interesting experience with AWS Cognito User Pools. It typically registers unique email IDs to identify users, and if you attempt to register with the same email, it throws an error indicating that the user already exists.

However, a friend and I simultaneously used the Auth.signup function with the same email but different passwords. Surprisingly, Cognito registered both users with the same email. When we tried to log in, it allowed access for my friend, who registered first, but I encountered an 'incorrect password' error.

I decided to delete my friend's entry from the user pool, thinking that I could now log in. To my surprise, Cognito considered my account non-existent.

This behavior is quite unexpected, and I'm unsure if it's a bug or an intended feature.