I don't know if this has been asked, most likely has, but I have been searching for ages on this forum and still can't find it...

So anyway...

I am making a map, it has a dome in it. At first I cut a sphere in half and hollowed it out, but some of the walls would go away after I saved it. So I made the dome myself.

So I use the vertex tool, too line up all the sides, so there will be no gaps in the walls of the dome. Then I save it. Then once I load the map up, some of the wall un-aligns theirself, so I try to align it again, then save it, same thing happens.

I had this problem myself a few weeks ago. The brushes ARE valid according to Hammer and will compile ok, but when the vmf is saved and reloaded one or more verts have slightly moved position. This continually happens; fix it, save, reload, and it's decided to move the vert again out of position.

The only solution I found was to delete the problem brush and remake it with 2 simpler brushes (i.e. the old HL1 method of creating terrain with back-to-back wedge/pyramid brushes).