If a bsp is turned into a static mesh and then the original mesh in the level is duplicated, it will register as duplicated in the world outliner but the mesh will not appear until re-assigned in the details pane.
1. Open Editor (any project)
2. Create a bsp box in viewport (lmb bsp box in placement>bsp mode and drag to viewport)
3. In details pane, select "Create static mesh">ok
4. Alt+LMB transform widget and drag to create a duplicate of the mesh
A copy of the mesh is created but will not be visible until the mesh is re-assigned in the details pane.
A duplicate is created and the mesh is visible in viewport.
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