AttachTo + ChildActorComponent breaks on static mesh actor BPs with physics enabled

This seems suspiciously similar to parts of what was reported in Collision and child actor - World Creation - Epic Developer Community Forums and AttachTo not working on USphereComponent - Programming & Scripting - Epic Developer Community Forums – especially latter.

boil-down of it is that if I create a (moveable) static mesh actor BP that has physics enabled, and then try to use it by calling AddChildActorComponent + AttachTo targeting scene default root, AttachTo appears to completely ignore(?) its transform handling option, and treat it as if it were “keep world position”.

Steps to reproduce:

  1. Create a BP extending StaticMeshActor
  2. Set BP defaults to be movable, enable physics, and set collision presents accordingly
  3. Add a tick event handler that applies a physics force (torque is main one I’ve tried at this point)
  4. Create a BP extending Pawn
  5. Add an event handler for play begin
  6. To that event handler, add an AddChildActorComponent node set for manual attachment and a non-zero transform vector
  7. Then add a node which attempts to attach that component to scene default component, set to keep relative transform
  8. Place an instance of pawn BP into a level at some position other than origin, and hit play

Expected result: pawn should spawn into level, with static mesh BP offset from pawn origin by transform vector specified in step 6, in all cases

Actual result:

  • If static mesh actor BP has physics disabled, it is spawned in correct location
  • If static mesh actor BP has physics enabled, it is spawned at that offset from world origin, rather than pawn’s origin

I have a sample project that demonstrates this in multiple ways, but I wasn’t able to find a good guide for “how to provide an example project sanely” anywhere – if someone can point me at instructions for that, I will attach it.

Of course, upon posting question, “similar questions” sidebar comes up with ChildActor with physics spawns in incorrect location - World Creation - Epic Developer Community Forums which appears to quite possibly be identical.

Why that never came up when I was searching for answers in first place, I have no idea, but it didn’t.

Hi JAelwyn,

Yes, I believe you’re experiencing same issue reported in ] (reported as UE-18762 in our bug tracking system). I’ve updated bug with your notes and I’ll post here if I see an update on it.

For future reference, best way to get a test project to us is to upload it someplace like Dropbox or Google Drive and then post a link for us.