The site won't let me choose 1.18 Experimental Snapshot 1 as affected, so I chose 1.17.1.

The bug

Even though worlds created in versions before 1.18 Experimental Snapshot 1 can't be loaded in 1.18 Experimental Snapshot 1, the "Don't forget to back up this world before you load it in this snapshot." warning still affects worlds created in versions before 1.18 Experimental Snapshot 1.

How to reproduce:

1. Drag a world created in a version before 1.18 Experimental Snapshot 1 in your saves folder.

2. Notice how it says "Don't forget to back up this world before you load it in this snapshot." even though the world can't be loaded in 1.18 Experimental Snapshot 1