planetmaker opened the ticket and wrote:

Steps to reproduce:
- Find a savegame with preferrably one missing newgrf, stored elsewhere, navigate to it in the load game menu
- now make the newgrf available in the search path
- open the newgrf dialog from the load game menu, rescan files. The newgrf now should be available, the game be reported as having no missing newgrfs anymore.
- close the newgrf dialog, the load game dialogue will still report it as missing newgrfs. The previous step can be repeated without a change

Version: r20210

Reported version: trunk
Operating system: All

This issue was imported from FlySpray: https://bugs.openttd.org/task/3969