How to repro:
1. Download the attached Fern.unitypackage and import to an HDRP Unity project using a 21.2 Editor.
2. Create a Terrain tile in scene, and add the Fern_Var0_LOD0 prefab to Paint Details brush
3. Start painting this on terrain, will notice the ferns look darker on Terrain
4. If add the prefab to Scene directly, will observe the different rendering results as shown in the attached Detail_Lighting.png.

Expected result:
No lighting difference.