Interiorinstance inside Interiorinstance

#1 It can create zoning issues, especially when lighting a mission.

#2 Could u please elaborate?

#3 Interiors have zones to determine what they can see from portals within themselves and from the outside. When you start putting interiors inside interiors you create an "unstable rift in the space time continuum" and it just wont work in Torque. If you need to put something inside another do it in Constructor / QuArk et al first. Also make sure interiors such as buildings don't overlap.