Example video: https://streamable.com/osbm2
Repro:
1) Bring up a cursor to place a buildable object
2) Click to place the signpost to begin construction
3) At the same time the signpost is placed, move away
Notes:
- I'm running Amber client in this video but confirmed it works and carries over with the classic client (i.e. these aren't just clientside ghost GOBs)
- The signs disappear as normal if you open them and then walk away without putting any materials into them