Hi Fred, this was fixed in 4.21 at changelist 4220571. I just tested your steps in the 4.22 preview and it works ok. Here’s my test case:
Before attaching (see pic), I have a cube and a skeletal mesh, both in sequencer. Take note of the existing transform track on the cube.
After attaching (see pic) to the pelvis of the skeletal mesh, the cube stays in place. Take note of the transform track values of the cube. They have changed to compensate the addition of the parent transform.
The change in the transform track of the cube is necessary. If there’s no existing transform track, sequencer will create one and add the compensation to that transform section. If there’s an existing transform section without keys, the compensation will go to that transform section. Otherwise, an additive transform section will be added and the compensation will go to that additive transform section.
If you have a test case that doesn’t work, please let us know. It’ll probably help to have a test case/project. Unreal Engine Community