I have a model under construction - this is ok but I've done something to the way it relates to other objects in the 3d view. With just the model in the view all appears to be fine when I rotate the view in any direction. If I add two new objects to the scene and rotate the view, the new objects move as expected in relation to each other but the model always appears to be in front of the other two objects - it never passes behind the other two objects. If I duplicate the model, the two models behave as you would expect but both are always in front of the others in the scene. I think I've set some parameter on the model but I can't see it!
It sounds like you've turned on X-Ray display mode for your object. You can toggle X-Ray mode under the Object properties tab > Display Rollout.
X-Ray display draws the object in front of all other objects (which don't have X-Ray enabled). It is most often useful for armatures to keep them from getting lost inside the meshes they control.