An InstancedStaticMesh component set to Stationary doesn't register overlaps. However, overlaps are registered on Static and Movable.
There is also an issue where actors that start overlapped with a InstancedStaticMesh will not be registered, but this is working correctly in Main 4.15.
I noticed that static meshes report overlapping actors mostly correctly, but for some reason, instanced meshes sometimes report overlapping actors, and sometimes do not report anything at all, and this can be affected by mobility setting. I'm not sure if this is intentional, so I'll just proceed to report this as if it's a bug.
If everything was done correctly, then every 0.2s, it should print nothing. If you move the pawn over the blueprint, then it should print the display name of the pawn actor. I expected this to print the names of overlapping static meshes and other blueprint actors, but apparently it does not do this unless something moves on top of the blueprint - such as a pawn.
Now, go back to the blueprint and change the mobility setting of the Instanced Static mesh to "Stationary". Now if you test, it won't print anything, even the pawn actor. Everything is ignored.
Setting mobility to "Movable" produces the same result as "static".
So, long story short, "Movable" and "Static" only report the pawn, or actors that move over the blueprint. Actors that do not move do not get reported as overlapping.
This contrasts the behavior of a simple Static Mesh Component, which reliably reports all overlapping actors, including non moving ones, in all 3 mobility states.
1. Open the attached test project
3. During simulation, select the StaticMesh on the right
4. Using the translate tool, drag it left and right through the InstancedStaticMesh
Results: Nothing will print to the screen
Expected: For the overlapped actor to print to the screen when the actor is overlapping with the InstancedStaticMesh
5. Stop Simulating
6. Open 'BP_Actor01'
7. Select the InstancedStaticMesh and the root, then change the mobility to Moveable for both
8. Compile & save
9. Repeat steps 2-3
Results: The overlap will print to screen as expected
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