BSP brushes only move in relative space instead of world space if the user has selected vertices from more than one bsp brush. User cannot change translation to worldspace instead of local space.
1. Open Editor (any project)
2. Create 2 box brushes
3. Open edit mode
4. Rotate one box 90 degrees (to see example clearly)
5. Select one vertex from each box
6. Use arrow keys to move left and right
Head over to the existingAnswerHub thread and let us know what's up.