No clef change appears at start of system with "Create clef for all systems" turned off

Ubuntu 14.04, GIT commit: e255575

1) new score, treble template
2) turn off "Create clef for all systems" option
3) add bass clef to measure 5 (first measure of second system)

Result: courtesy clef appears at end of previous system, but the clef change at the start of the system is not displayed. I think it should be - turning off "create clef for all systems" should not affect clef *changes*.

I can guess hwy this is happening - the code controlling the display of those clefs is checking the "generated" status of the clef, and this clef in fact *is* generated, since the courtesy clef is the "real" clef (clefs are funny that way, as they normally appear before the barline when not at a system break). We need to somehow check whether this represents a change - maybe by checking the clef map.