This is actually a lubuntu-artwork problem as although I cannot reproduce it in an up to date wily xubuntu system with the xubuntu theme but if I install the lubuntu-artwork pacakge on xubuntu and set lubuntu default as the theme I apply the change and can reproduce the problem. However working around this on lubuntu is made more difficult because bug 1464899 makes me unable to graphically change the theme in lxappearance.
This is actually a lubuntu-artwork problem as although I cannot reproduce it in an up to date wily xubuntu system with the xubuntu theme but if I install the lubuntu-artwork pacakge on xubuntu and set lubuntu default as the theme I apply the change and can reproduce the problem. However working around this on lubuntu is made more difficult because bug 1464899 makes me unable to graphically change the theme in lxappearance.