building collision being fiddly

I'm making a map, and I spawned in a pre-built structure (one from pavlov's) but the collision isn't working on it when I play it in the editor. It stops bullets and grenades well enough but I can still walk through the walls for some reason. I set it to 'block all' via the right-click menu but it's still refusing to let me walk around it. Can anyone help? is this something that gets fixed when I build fully? Will I have to build BSP buildings of everything? :(