The dotted border is kind of the problem. It represents an active connection between the current spreadsheet and what was copied, and that connection shouldn’t exist.
When implemented normally, ‘copy’ puts a copy of the selection on the clipboard; ‘paste’ takes whatever was on the clipboard and puts it at the current location.
Once you copy, it shouldn’t matter what you do on the spreadsheet, because you’re pasting from the clipboard.
Normal behaviour can be emulated by copy+pasting into a blank spreadsheet when you want to copy, and then copy+pasting from there when you want to paste.
But then you’ve just turned that spreadsheet into what the clipboard is supposed to be.
When implemented normally, ‘copy’ puts a copy of the selection on the clipboard; ‘paste’ takes whatever was on the clipboard and puts it at the current location.
Once you copy, it shouldn’t matter what you do on the spreadsheet, because you’re pasting from the clipboard.
Normal behaviour can be emulated by copy+pasting into a blank spreadsheet when you want to copy, and then copy+pasting from there when you want to paste.
But then you’ve just turned that spreadsheet into what the clipboard is supposed to be.