Steps to reproduce:

1. Select any cell.
2. Attach a comment to this cell.
   ( right-click the cell and choose 'Insert Comment' ) 
3. Type any text in the box (callout) that appears.
4. Click outside the box to close it.
5. Show the comment.
   ( right-click the cell, and choose 'Show Comment' )
6. Double-click the comment text to edit it.
7. Place the mouse pointer outside the commment,
   press and hold down the left mouse button
   and move the mouse.


That creates a text box - rather unexpected effect.