Listen server doesn't show up in master list, but friends can join via IP.

This is pretty annoying, I forwarded all my ports, and friends can join my GMOD Listen server without problems, although my server doesn’t show up in the master server list, so most of the times I’m alone lol!
When I check my LAN games screen, my server shows up, with my static IP adress (192.168.1.100)

Is there a way of fixing this? am I missing something here?