Yep, looks like it’s doing something similar on mine too, after updating to Unreal Engine 4.6 I zoomed in and noticed the BSP brushes I used for cutting doorway openings was raised along the Z-Axis by exactly 0.5, I went ahead and added the 0.5 for the Snap Sizes, the auto-snapping to grid didn’t work, and used the 0.5 to manually re-position and align it properly back to floor level, and the dropping to floor stopped working for new BSP brush geometry.