Speaking as an ex aircraft engineer (and now pilot) it sounds to me like the throttles on that particular aircraft were set up with maybe a little too much 'bounce'. That is a term used in the setting up of controls (be it flying or otherwise) to ensure full range of movement at the end unit and not just at the throttle quadrant or yoke for example.
Talking about throttles, when you retard them, 'bounce' is felt when the engine idle stop is contacted first, and further rearward throttle movement is then made by the pilot until he hits the mechanical stop in the quadrant. The difference between these two stops means the control run flexes and this is what you feel. We are only talking millimetres of movement here and so is not normally that noticable.
Hope this helps..