Thanks for the reply Remi.
I'm referring to the toolbar element in the "Custom interface..." window labeled 'Trickplay Reverse'. When I say it doesn't work, what I mean is that it doesn't appear in the toolbar after you add it to a toolbar and close the toolbar editor window. Other toolbar elements that I add appear and work fine.
Regarding the underlying functionality, which I believe probably is negative playback rate that you are referring to, I've seen it work before (and have used it) in older versions of VLC.
And if we are talking about the same thing and you say it will never work, why is it in the GUI?
Thanks,
Ryan