lens - How commonly do constant-aperture manual zooms actually influence the aperture mechanically when zooming?

I have seen a few examples of constant aperture zooms (eg a 28-100mm f/4 Ricoh.) in the secondhand markets where the aperture appears to be not fully open (visibly non-round hole) at some zoom settings. Did some designs actually do that intentionally to enforce the constant aperture, or are these just cases of mechanical defects where unrelated mechanical parts interfere with each other due to friction or bad justage?