Attachment was not pasted to the cell after copying

[biallenchanuow]

Environment
Jupyter Notebook version: 6.3.0
Conda version: 4.10.1
Python version: 3.7.10
Platform: Mac OS version 10.15.3
Browser Version: Google Chrome - Version 90.0.4430.212 (Official Build) (x86_64)

Description
I encountered this issue when I uploaded an image onto a Markdown cell, created another Markdown cell, selected Edit->Copy Cell Attachments, then selected Edit->Paste Cell Attachments to the new Markdown cell. A line of text "Type Markdown and LaTeX: 𝛼2" showed up in the new cell. And after double-clicking on the cell, the cell type was changed back to "Code", but no attachments were pasted. I tried the same steps with a LaTex file and the same thing happened. Does anyone know if this related to the attachment handling module(s)?

Failure.6_attachment_not_pasted.mov

[jtpio]

Thanks @biallenchanuow for reporting.

Tracking this in jupyterlab/jupyterlab#14663 so it can then be consumed here in Notebook 7.