Problems with rendering 2D Sprites

Hi, im having trouble with rendering 2d sprites on a plane mesh, im using a similar technique as in this topic:
http://forum.unity3d.com/viewtopic....postorder=asc&highlight=spritemanager&start=0

the only difference is I use one renderer for each sprite object, so its basically just mapping pixels to uv space on a plane and using particles/alpha blended material /shader.

The problem is when I put some objects on the scene, as the camera is scrolling, some objects near the edge of the screen popping in and out (they disappear when the transform is out of the camera, but the sprite itself is supposed to be still visible), does anyone know how to solve this problem? thanks.