BSP Building problem

Hello guys

I have now a huge problem what affect my level designing project. Like you see in the picture when I choose a BSP brush, in this time this ground plane, the “triangle” thing (what ever it’s called) goes inside the mesh.
So example if the object is bigger than the triangle, I cannot move it at all since it’s inside the object. Also all the corners has this weird “lights”. Is this a setting what has been turned on somehow or a bug. I just recently
updated to 4.6.1 and I don’t like the update at all.

Can you help me?