Summary: When moving a ‘ghost’ item (i.e. the translucent model visible before it has been placed) it will be placed properly, but appears in the stockpile. Placing the item from the stockpile removes the originally placed item.
Steps to reproduce:
- Build something (chair)
- Select chair and place it somewhere.
- Before the worker can physically move it to the designated spot, click on ‘Move Item’ button.
- Place elsewhere.
- Wait for worker to place it in the newly designated spot.
- Open ‘Place Items’ window (P)
- There will be one chair in stock. Place it elsewhere.
- Observe original chair.
Expected results: When the chair is moved before being placed, the worker will carry it to the new location, without any change in unplaced stock.
Actual results: 
Not seen in this photo but I had moved the bottom-right table over by one square, as I had misaligned it. I noticed an extra table in stock (I had only crafted 4), and placed it in between the upper- and lower-right tables. Disregard the table to the far-right, it was where my mouse was pointing, and had not been placed.
A worker arrived, picked up the upper-right table, and moved it to where I had designated. Stone table stock dropped by 1.
Notes: I’ve recreated this bug many times, but couldn’t figure out what was going wrong. I don’t know if there’s any significance to the upper-right table being removed. If its of any use to you, it may have been the second-to-last placed table - i.e. it was placed third, just before I realigned the bottom-right table (which was placed last).
Version: latest on Feb 7… x64