I needed some temporary squaring pieces for a frame I’m putting together, so I opened a new design and created a 6" square using the design tools, then added a line bisecting it diagonally. Then I selected both shapes and copied/pasted them. This created a third thumbnail-less object in the settings list on the left:
If I select a material, I can hover over the blank object, and then it turns out to be one of the squares.
So…the lack of thumbnail is weird, probably a bug? The fact that copy/pasting a square creates a second object while copy/pasting a line keeps the copy and original as one object seems inconsistent, not sure if that’s a bug or a “feature.”
Browser info: https://whatismybrowser.com/w/JJFTX98