Wen you have a dropper pointing in to a chest full of items and you try do send more items trow the hopper they will just disappear.
If you put a stack, then power the dropper, that stack will be reduce to one item. Flow the screenshots for better understanding.
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dropper*
And I could see this being a serious bug.
Duplicate of MC-7654, please use the search function to see if your bug has already been submitted. Currently over 50% of tickets are being closed as duplicate.