Repro:
1) Add a script to e.g the Main Camera
2) Change the script using ObjectSelector
3) Notice that the cogwheel disappears and context menu is not available on right click.

We found that the editor.target is null for this editor (component) and that the regression is caused by b51b8ace823c ("Fix monobehaviour == null returning true if there is a monobehaviour with that instanceID but it is not actually referencing the right object. case 539463")

Outcommenting the following in ScriptingObjectOfType.h fixes this issue:
if (temp->GetClassID() == ClassID(MonoBehaviour))
return false;