Small light pieces may move if they are not secured in a suitable approved rack or accessory. An overturned container can then fill with water and shelter its inside surface.
Understanding this situation
Only dishwasher-suitable plastic should be used, and the permitted rack location depends on the appliance and item instructions. A generic top-rack rule does not apply automatically to every model.
A useful next step
Use the designated supports or a compatible small-item container where permitted. Do not improvise metal ties or obstruct spray arms. Describe whether the item moved when evaluating a poor result, rather than assuming the appliance failed to clean an unchanged position.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.