f21 BETA version of LXDE... A right-click anywhere on main screen opens right-click-menu way up in the upper left of the screen. Should be nearer location of mouse click. Also, trying to "create new" --> "empty file" seems to frequently do nothing. (It does seem to work sometimes). Right clicking on a desktop icon (e.g. for file) also opens menu in far top left. If menu extends over mouse pointer, you must keep right button down for menu to persist. If menu does not extent to mouse pointer, the menu is sticky. Left or right clicking in screen center should make sticky menu disappear, but it does not. Seems like you must pick something on the menu to make it go away.
I've got a KVM's guest system which runs Fedora Rawhide with LXDE. I experience the same issues Bill reported. Standard Openbox's menu seems to work as expected on a LXDE's session. My lxcommon's version is "0.5.5-0.10.20110328git87c368d7.fc21.noarch". Feel free to ask me further details, if you need.
Fedora 21 LXDE Install - Same problem with menu popup location and "Sort Files" menu options do nothing. .xsession-errors logs the following (pcmanfm:804): Gdk-CRITICAL **: gdk_window_get_device_position_double: assertion 'GDK_IS_DEVICE (device)' failed
I have the same issue with a new user who has nothing in the home directory.