The Bug

In creative mode, if you have an even number of a certain stack of blocks in your inventory, halve it by right clicking, drop the stack left in your inventory with strg+q (that's on my german windows laptop, don't know about other types of keyboards, might be command q) and then quickly place back the part picked up, the thing you dropped will disappear when you pick it up. As long as the number of items is even it should happen, only tested with ladders and spruce planks. (difficult to explain, video should be linked as it is too big to attach). I had the same issue when tested in 1.17.1 . Just to add, doing this with an odd number of blocks will not work from what I have seen in my tests. https://youtu.be/sVFZYRySomU 

Reproduce

• Get two items
• Go into the Survival Inventory
• Pick up the two items and press q

Observed Result

The item was deleted

Expected Result

The item wouldn't be deleted