Thank you for pointing this out, I was able to reproduce this display issue on our end. We will report it to our engineering team to review. As a workaround, if you refresh your browser after you edit the project variable, you should see that the results do update in the "Display Variable" tile. Please note that once you commit the change, the variable will immediately update in the system and you can confirm that by navigating to Project Variables (More options -> Variables).
If this does not work for you, would you mind sending us a screenshot of the "Edit project variables" tile?