So, here's the bag of plums

I loaded up Garry's mod to fly around in this sexy blue box, and until the official Dr. Matt interior gets finished, I'll use this one

Buutttt..... I can't, I open the doors and see.... well... this

SCREENSHOT OF BUG:
http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=735420596

PS. I've downloaded everything required, models, textures, etc. I've got absoloutely EVERYTHING... and this still happens, when I actually walk in to the TARDIS, I fall for a second or two and land OUTSIDE the TARDIS, This is really bugging me