This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
This issue was originally reported specifically for Destructibles, but it appears to affect Skeletal Meshes, and static meshes when selected. When "Render in Main Pass" has been disabled skeletal and destructible meshes will show a noticeable artifact with shadows visible through the mesh. Think of it similar to looking through a portal the way this affect looks.
Tested in the following builds:
1. Open any UE4 project
2. Use the Default level with Stationary Light already built
3. Add any Skeletal or Destructible Mesh
4. Select the mesh and in the Details Panel uncheck "Render in Main Pass"
Result: Noticeable shadow artifacts when using Stationary lighting that does not have a far enough Shadow Distance compared to the size of the asset.
Expected: No artifacts visible through the asset when removing from the Main Pass.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-29576 in the post.