It looks like I'm having the same problem: I log into LXDE, click the "PC" button and I can only see "Run" and "Logout". I click "Run", then the Run Window pops up. I hit "Cancel". Then I click the "PC" button again, but now the whole menu shows up. So, for me it's reproductible.
EDIT: I run PCLinuxOS-LXDE-2012.12, fresh install.