I think I've reported this issue on WoWInterface, but better to report it where it matters. :)

When in a vehicle the backdrop (if you have one of course) doesn't hide.

Before the vehicle: http://cl.ly/3F3y/content

In the Vehicle: http://cl.ly/3FWk/content

I've set the backdrop to the Rested Frame.

I fixed it in the post update, but I think it's worth it to open the issue anyway:

-- Experience Bar Pre Update
local ExperiencePreUpdate = function (Experience, unit, min, max)

    if unit == 'vehicle' then
        Experience.Rested:SetBackdropColor(cfg.bdc.r,cfg.bdc.g,cfg.bdc.b,0)
    else
        Experience.Rested:SetBackdropColor(cfg.bdc.r,cfg.bdc.g,cfg.bdc.b,cfg.bdc.a)
    end
end

Test if it still occurs after 67d4967