DetachmentRules is not applied when WhenFinished of AttachTrack is set to RestoreState.

Purpose:
Create a parent-child relationship using the “Attach Track”
After that, I want to release Attach in the middle of the sequence and leave the child.

Set "When Finished" of "Attach Track" to "RestoreState",
I thought it would be possible if "DetachmentRules" was set to "KeepWorld", but it did not behave as expected.

When "Attach Track" "When Finished" is set to "RestoreState",
MovieScene3DAttachTemplate.cpp
Although it seems to maintain world coordinates by F3DAttachTrackPreAnimatedToken :: RestoreState ()

after that,
Coordinates before attachment are restored by FMovieScenePreAnimatedState :: RestorePreAnimatedState.

Licensee pointed out that "DetachRule" does not seem to make much sense in the current operation.

Purpose:
Create a parent-child relationship using the “Attach Track”
After that, I want to release Attach in the middle of the sequence and leave the child.

1. Create a "Level Sequence" and create an "Attach Track".
2. Create a parent-child relationship.
3. Set "When Finished" to "RestoreState" and set "DetachmentRules" to "KeepWorld".

Result:
The child returns to its original position.

I attached a project file.