No glitch there, it's where they congregate. it IS a party after all 
Please read my FEAR/Portal/HalfLife Fan Fiction!
Repurposed
Yup it's normal. 
Yep. Sometimes they move to the tram, sometimes they move to the various entrances, other times they just sit there.
Made my Spine scrapper very happy one day. Heck, my (fortunately higher than them) Emp/Psi did quite the number on them once...
http://i3.photobucket.com/albums/y72...2-07-19-15.jpg
http://i3.photobucket.com/albums/y72...2-07-21-03.jpg
Very crazy glitch I came upon. There were well over thirty SupaTrolls just hanging around. Then I aggroed and had to fly away very quickly. I wished I had taken more screen pics.