Code macro output content corrupted after partially parsing other code macro content from other page

Here is the reproduction procedure:

1. Open (view) a page with already has a code-block
2. Mark some text and the code-block and copy it. screenshot:selection.png
3. Create a new page, insert the content from the clipboard (you will notice that the inserted code-block does not look like a code-block). screenshot:output of simple copy.png
4. Create a new code block in the page and copy the content of the corrupt code-block into the new. screenshot:output of parse in the code macro.png
5. Delete the corrupt code-block
6. save the page. screenshot:output after saving the page.png

I also attach the original source code (original source.png) and corrupted page source code (corrupted source.png) for a review.