Description
Due to a problem in the Intel® Quartus® Prime Standard Edition Software version 21.1, you may see this problem when using the shortcut key combination Ctrl C / Ctrl V to copy and paste in the Text Editor.
Resolution
To work around this problem, use the shortcut key combination Ctrl + Insert / Shift + Insert to copy and paste.
This problem is fixed starting with the Intel® Quartus® Prime Standard Edition Software version 22.1.