The direct link is finicky at times, especially on mobile devices, they don't seem to want to redirect to the index file sometimes. Otherwise for the second part of your post, if the link is non existent on the site, then you will be automatically redirected to the forums. Any non-existent page like /slkdfhjsldkfjh or /f will redirect you to the forums, hence why removing the / and S works.
Cheers,
