rakarrack version 6.1 (did't look in current git version but I assume its unchanged):
at the end of Vibe::changepar():
fcross = 1.0f - abs(flrcross);
abs is the integer form, so fcross will nearly always be 0.0 (1.0 at the ends of the range).
I think it was meant to be fabs (or std::abs), though its not a dramatic difference in sound.
Btw. I have included the vibe code in guitarix - thanks a lot :-)