No, I didn't touch the lxde-rc.xml file, and the hotkeys definie there did not work.
I had un-installed some package like wireless and bluetooth stuff since I use a desktop compt. So I thought its wasn't needed.
Doing so, I must had un-installed something (a lib ? ) that affect the hotkeys 'deamon' (not sure how is it handeled).
That's the only reason I can think of.
But is you have some more idea, I'm be happy to ear them !
PS : Take notice : since I do a re-install -and this time I leave all the should be unsed packages. SO I can't test anything. When I have some time, I will un-install them one by one and see what happen