User Coordinate System Problem

Hello,When i use UCS icon, then i select a UCS, Planar UCS, let's say Left side...and after that when i use real time zoom or pan, the 3D model toppels over in all the directions. it's a problem that appears very often.Let's add that the entity snap doesn't work very well in 3D.I'm working on 3d models often via architecturals and that becomes difficult with these problems ...what can i do ?Thx - R. Stas