lxsession violates the Freedesktop.org autostart specification by ignoring the custom *.desktop settings under ~/.config/autostart in favor of those under /etc/xdg/autostart.
The issue was observed on trusty release of Lubuntu with the latest updates (lxsession version 0.4.9.2+git20140410-amd64). Because of this issue with lxsession, "lxsession-default-apps" command doesn't work as expected.
Steps to reproduce:
Updating system-wide "/etc/xdg/autostart/nm-applet.desktop" to include "LXDE" in "NotShowIn" setting does disable nm-applet from automatically starting up (as expected).
Freedesktop.org autostart specification states that:
"If the same filename is located under multiple Autostart Directories only the file under the most important directory should be used.
Example: If the two files /etc/xdg/autostart/foo.desktop and ~/.config/autostart/foo.desktop exist then only the file ~/.config/autostart/foo.desktop will be used because ~/.config/autostart/ is more important than /etc/xdg/autostart/"