If you have changed it in the control panel and it's still the same you need to go into the Logitech Profiler, then click "Edit", then go to "Specific game settings...", then half way down you'll see "Report combined pedals", uncheck the box. Also, there is a setting in LFS controller options for seperate axis for brake and accelerator, you'll need to make sure that is selected too.
If you don't get it try this, it's basically what I've said but with a couple of pics to guide you.
Setting up a Logitech Wheel