This has happened once.
I decided I needed nuclear reactor faster, so put an L3 assembler on top of an L2 assembler.
HUNDREDS of pieces of concrete, red circuits etc spilled on the ground.
I haven't tried to reproduce this, it's the only time its ever happened to me.
At the time, I was playing multiplayer and FPS/UPS was just starting to drop as the other player was engaging some huge biter nests. So possibly to do with an UPS glitch?
[0.15.21] Items spill on ground when upgrading assembler
Re: [0.15.21] Items spill on ground when upgrading assembler
Oh I'm sorry forgot to search, it was so unusual. :facepalm: