Found an artifact in Stronghold Demo

After the installation of TGEA, I open up the Stronghold demo and then launch the mission -> Content Pack Demo 1.... Then I Found this

http://img503.imageshack.us/img503/5572/strongholdbug1xu5.th.jpg

http://img145.imageshack.us/my.php?image=strongholdbug2ga4.jpg

Please, anyone can explain this?