Account dosen't delete after being not activated with email in 24 hours since it was created

Steps:
1) Enter the valid Username, Email, Password and Captcha and click the sign up button;
2) Check your email for activating account message, but don't activate it;
3) Wait 24 hours;
4) After 24 hours try to sigh up again with the same valid Username and Email.

Expected result:
You'll see the message to check your email to activate your account.

Actual result:
You'll see the message that account with this Username and Email has already created.