This seems to occur in survival and creative, and with various openable block entities such as chests, shulker boxes, and hoppers. First, give yourself several stacks of an item. Open your inventory, and hold Ctrl+Q (or whatever your drop item key is set to). Drag your mouse over the stacks of items, and observe that each stack is dropped as soon as the cursor hovers over it, without needing to re-press the Q key. Now, pick up the items, and place a chest. Open the chest, and attempt to drop the items similarly (it doesn't matter whether or not you move the items to the chest, just that you have the chest open.) You will observe that no items are dropped unless you type the Q key while hovering over each stack.

While there are obviously two ways to resolve this inconsistency, I would highly suggest extending the rapid item dropping behavior to all cases as it can be quite useful and less tedious than the alternative.