Additive BSP Selections Acting Grouped after Building Geometry

After building geometry with multiple box brushes stacked on top of one another, the selection no longer isolates a single brush but acts like all of the brushes are combined.

This issue can be resolved by simply moving one of the brushes. It will then allow you to select individual faces on each brush.

Regression?
Yes, this does not occur in the binary release of 4.12.5

1. Download and Open attached project.
2. Press the 'Build All' option.
3. Attempt to select an individual box brush within the scene.

Outcome The selection highlight encompasses all the faces of the box brushes along that plane.

Expected Only the face of the selected brush is highlighted.