The behaviour that you are currently observing with SpreadJS is the design behaviour of SpreadJS, where in it implicitly cancels the ClipboardPasting event when the user tries to paste an invalid range of cells in SpreadJS. Hence, the ClipboardPasting event cannot be used to handle this scenario.
As depicted in the HTML Page attached above you would need to handle the keydown event to capture, when the user presses the Ctrl+V shortcut to paste the copied contents. And manually handle the paste operation for the cells by adding the additionally required rows and columns.
Could you please let me know what issues are you exactly facing with the custom implementation provided in the HTML Page attached above so that we can accordingly look into the issue further.