I was just wondering if maybe it was an apache problem or to see if you had gotten help with RewriteMatch. We're not an Apache help forum, that's why I was asking. But if you feel it's a roundcube problem fine.
There is no "loading" div for the login. Reason is is that the login is not AJAX whereas the sending, loading, and all that stuff really is. So what you're seeing is the proper default behavior.
If I have time today, I'll look into it and see if I can't submit a patch to fix this issue (if it hasn't already been fixed).