3ds max Attach poly problem with Occlusion Culling

I'm creating street scene in 3ds max, I have some simple planes with textures of houses, and one house model for higher resolution, I am building it from smaller blocks with same texture to get higher resolution of the wall. Before exporting I convert one of the blocks to editable poly and attach all other blocks of the house to it to get only one object and reduce drawcalls.Actually the front of may house contains two objects then. Problem starts with occlusion culling - it hides one of these objects when it is in camera view. For me it looks like it behaves as there was only that one block, which has all others attached. At some angle near the wall the missing object appears... Also, it contains blocks which are made with mirror function, if it has something to do with this, but it shouldn't, because everything is fine in editor.. Thanks for your help in advance!