Hammer Editor Messing Solids Up

You have bad brushes in your map, probably due to erroneous vertex manipulation. .bsp s save brush info as points and vertices, but within hammer brushes are defined as sets of planes (this is why brushes cannot be concave). The difference you're seeing is because hammer can't save your brushes as a set of planes.

The easiest fix to this is to cross-clip non-coplanar quad faces to make them into legal triangle faces.

Select a brush, then select the clipping tool. Use the clipping tool and cu the selected brush from corner to corner, there by forming a triangle.

Geometry class time: Any three points anywhere in three-dimensional space can be the corners of a flat triangle. Not every four or more points can be the corners of a flat shape. Imagine taking a piece of paper and raising one of the corners while holding the others down. The paper bends. When you use vertex editing to manipulate brushes, you sometimes "bend" the shape one way or another in a similar way. Hammer can't work with bent brushes. You need to cut it into triangles so that it "folds" instead.