Taboi:
sometimes the button could stop being active after entering the login and password
There are no additional scripting added to the login button, it's just straight «submit» in HTML source, so I couldn't understand how it could become inactive and for what reason. In opposite, there is javascript attached to the «Post message» or «Post topic» buttons, which disables the button after it's clicked. It's done to avoid multiple submissions on weak speed connections or network interruptions, when you have to wait for a long time and could be confused why your message is still not posted... But it's only for Post buttons, not Login (Sing in).