The fc modulators don't affect the key "0" (very left button on the 128-key keyboard).
a sample soundfont is attached. (velocity fixed to 127 for easy navigation)
Press the key-0 and wait a few seconds (because of there is a single sample, it is necessary to wait for the attack time in low-keys).
Then test with the keys next to it. (1, 2, 3, 4 etc.)
Test from Medium-C (60) to bottom (0).
You will see that the 0 key is unaffected.
PS: Maybe it's not important because its just about the 0 key.
But, If it affects the calculation, it shifts (or multipy) everything else forward .
Wow thank you for this finding. It's fixed!
In the beta version key and velocity are shifted by 1 (0 becomes -1...). The fix will be in the release 2.1.