See if you can reproduce it this time:
Default settings.
Enable “Middle Click to Paste”.
Find in files.
Middle Click in the find-in-files result.
Middle Click.
▲ This step (paste) is not saved in the Undo history.
(“Redo” in the above post should have been “Undo”.)

Disable “Middle Click to Paste”.

Active String setting:
URLs: Middle Clicked event: Action: None + Select String before Action

Focus Find toolbar.
Middle click a URL in the view.
The URL is selected.
** But the focus is still in Find toolbar.
The immediate Ctrl+C (to copy the selected URL) will miss.

So please also make middle click set focus in such cases, which I think is a “natural” behavior.