When clicking on a actor in the World Outliner while the Details tab is docked to it, it switches over to the Details tab. This bug was not present in 4.17.2 but is in 4.18 and 4.19.
Result: It jumps to the Details tab
Expected: It remains on the World Outliner.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-53611 in the post.