This is a sort of catch-all ticket for problems with copying and pasting.
See:
- https://www.mediawiki.org/wiki/Topic:X0h7ihzschsqkuct in 2017WTE with and without CodeMirror syntax highlighting
- T200107: Pasting content sometimes scrambles it
- T316838: Please do not let the cursor jump to the top of the editing area when using Shift key after pasting (loss of focus?)