This is not described in the manual and doesn't correspond to any of the filter modes shown on the panel. Actually, this was not supposed to be possible at all!
After a brief moment of panic believing the instrument had gone nuts, I turned the keyboard off and on again, changed to a different program, came back... And still the LEDs were all on.
Checked the patch on the manual and guess what...it's named "Super secret filter pad"!!!

The guys at Clavia were smart in burying it into one of the last program banks...it takes a lot of perseverance to get there!

I checked on the internet and it's a known easter egg, but it's seldom mentioned and I didn't find that it was ever discussed here, so I thought it deserved its own thread.
You get to the secret filter by pressing Shift+Filter Type.
It seems to be a Notch+HP filter, and it also happens to sound great!
Resonance is very subtle and it doesn't go into self oscillation, but the sound is very full and it sits great with distorsion and/or unison.
My Lead2X never cease to amaze me!!!
