Problem with polyobjects?

[PsyFi]

Hi, i'm new to posting here, and i am making a map utilising polyobjects, when the polyobject is placed in a doorway, and opened it sort of "extends" into the next room, i have heard of a thing called midtex polyobjects, but i have not found any information. can anyone help?

[ramon.dexter]

Midtex polyonject is composed of linedefs with middlle textures applied. It is not void inside, but a sector.