Am I overlooking somthing ?
Modulating the pitch of Osc A( by envelope ) , also modulates the Pitch of Osc B
Choose init patch , set osc mix fully right ( so only osc B is heard ) , set pitch modulation for osc A to full .
Result: pitch Osc B is also modulated
Screesnhot

I believe this is because the frequency of Osc B is linked to Osc A, and any adjustments to Osc B's frequency are relative to Osc A. (see screenshots)

If a_mod has some non-zero value, and you don't want the pitch envelope to apply to Osc B, set b_mod to the same value as a_mod, then right click it and choose "Flip Value" (screenshot). This will cause an inverse amount of the same mod envelope to be applied, neutralizing it.