I found that if I selected a terrain, copied it and pasted it into a scene it was flat (not terrain) any attempt to click on it and move it gave an error message, my work arround was past, then edit (opening the terrain to edit showed an unmodified feturless terrain) reapplied the texture and went back to the assembly room and I could move it like you would expect, have not tried adding a terrain to the brouser yet.