Nah, Hammer does this with completely valid brushes too. For example, the pine trees on my map - I seriously don't know what's going on there. They're basically 3 cones on top of each other, with the bottom two clipped properly. Any time I open my map, it gives me an "For your information, X solids were not loaded due to errors in the map file", for every brush that represents the top of a pine tree. Which is a perfectly normal cone. So, I have to recreate every one of them every time I'm going to compile. I've shortened this hell by making the tree into a prefab, but it's still majorly annoying.