Pasting a file to write-protected folder currently gives no feedback to user but silently ignores the operation. There is no error or warning messages for this.
It may be better to show a dialog to tell that the operation is not permitted there.

REPRO STEPS:

(1) Insert an SD card which is write-protected.
(2) Open Files app open the SD card. (if it's not opened automatically)
(3) Choose one of the files in the drive.
(4) [Ctrl]+[C] to "copy" the file to the clipboard
(5) [Ctrl]+[V] to paste the file to the same directory

Result: nothing happens.


Note:
- when using drag-and-drop operation for copy/move, there is a visual feedback with icon next to the file tooltip (drop effect).
- when right-click on window or folder at step (5), "Paste" or "Paste into folder" menu item is grayed out in the context menu. This also works as a visual feedback.