Object Mixer shows actors the World Outliner hides (5.8 is incompatible with 5.7-and-earlier behavior)

For the same project and the same filter, Object Mixer returns a different set of actors on 5.8 than it does on 5.7. Actors that the World Outliner hides now appear in the Object Mixer list. Editor tools built on Object Mixer therefore behave differently after upgrading to 5.8.

The World Outliner itself is not affected. This behavior change came from //UE5/Main CL49143080.

Conditions:

An Object Mixer filter whose GetObjectClassesToFilter() returns AActor. That is the natural thing to write for a tool that lists every actor in a level.

Both Object Mixer surfaces are affected:

• Window > Object Mixer, with the filter ticked in its filter-class menu.
• UObjectMixerEditorUWidget placed in an Editor Utility Widget, with Object Mixer Widget User Config > Default Filter Class set to the filter.

The attached project reproduces this.

1.  Unzip the attached project and open the .uproject with 5.7.  LV_MixerRepro opens automatically.
2.  In the Content Browser, right-click EUW_MixerRepro > Run Editor Utility Widget.
3.  Confirm the actor count is 8 on the widget as weel as the Outliner panel.
4.  Convert the project to 5.8 and repeat step 1-2 with 5.8
5.  Confirm the actor count is 15 on the widget.