In «sign in» window, when choose from the username suggested items, form is submitted

Steps to reproduce:
1. Sing in using valid username and password;
2. Logout;
3. Click "sing in", start typing username you used in point 1;
4. When browser shows autocompete to choose, navigate over the suggested items and press Enter to choose username you used in point 1;

AR: error message «Your login attempt was not successful, try again».
ER: choice of the username is submited, cursor moves to the "password field".