It could just be the way the site is designed not being optimized for the size of your screen. You have a rather large screen yet it still counts as being mobile sized, so it's possible that the website wasn't coded correctly for a mobile screen that size. But I don't know. You could try and request the desktop version on your mobile browser and see what happens.
EDIT: Yeah I just tried it actually my making my window smaller. It just comes from the resolution of your screen. In that case you might want to try and switch to a mobile version or getting the Discourse (message board host) app.