The install prefix couldn't be overridden on the command line, the SET...

The install prefix couldn't be overridden on the command line, the SET overrode any value you specified. Adding the cache keyword to SET seems to have fixed it though. Is this a cmake bug?

CMakeLists.txt

@@ -34,7 +34,7 @@ IF(UNIX)
 	IF(APPLE)
 	ELSE(APPLE)
 	# Like all variables, CMAKE_INSTALL_PREFIX can be over-ridden on the command line.
-	SET(CMAKE_INSTALL_PREFIX /usr/local)
+	SET(CMAKE_INSTALL_PREFIX /usr/local CACHE PATH "")
 	# When used later, "bin" and others with no leading / is relative to CMAKE_INSTALL_PREFIX.
 	SET(KICAD_BIN bin CACHE PATH "Location of KiCad binaries.")
 	SET(KICAD_PLUGINS lib/kicad/plugins CACHE PATH "Location of KiCad plugins.")