When you hide all buildings or hide citybuildings, the front-images of citybuildings are still shown.
However, the same is not true for monuments, factories,... which lose their frontimage even if you only hide citybuildings.
Can you post a screenshot? I cannot reproduce this.
Top is regular view
Middle hides citybuildings. As you can see, the rubiks cube and the locomotive to the right as well as the flags at the townhall disappear.
Bottom hides all, but you can see the smoke from the chimneys.
All these examples are animated, but it's the same with non-animated frontimages.
(http://dl.dropbox.com/s/02ghzkkmpmfn1k7/frontimage_glitch.png)
It seems to me that this error has been from the beginning of time hehehe.
In fact, when urban buildings are hidden, for example, animations in the factories are lost, or some tall constructions are cut out.
It is old. But I couldn't find it being reported, nor a statement that it works as intended. For all I know, could be no dev is aware.
I cannot find these buildings with smoke. What are there object names?
Edit: Found them. Should be fixed in r8784.