This is how it behaves on my side (latest version from A4M):

• fill in valid login & password
• click on "Login"
• the progress wheel spins and nothing else happens
• when I click cancel, I'm dumped to a black screen

IMHO, it should return to the login screen if the user clicks cancel during the login phase or if the login fails for some reason. Also some login timeout - say 30 seconds - might be in order.