That's because the code roflmao456 posted also adds a full stop to any commands you type. This should work:
code:
function OnEvent_ChatWndSendMessage(ChatWnd, Message){
if(/[a-z\d]$/i.test(Message) && Message.charAt(0) != "/") Message += ".";
return Message.charAt(0).toUpperCase() + Message.substr(1);
}