Native OSC face tracking data opens the mouth on any ordinary avatar that do no supports full face tracking. This happens while silent, with Voice and Viseme both staying at zero.

Environment:

Windows PC, desktop mode.

VRChat 2026.4.1-1935-a61ceb9d89-Release.

Avatar: SeatTestCat.

Avatar ID: avtr_61c49ec4-0d80-45f9-a936-f7992d7148b8.

OSCQuery reports /avatar/avatarfullfacetracking as false.

Reproduction:

Enable OSC, wear the avatar above (or other ones that do not natively support ft), and open a mirror.

Send /tracking/face/v1 repeatedly (tested with 30 sends a second), with one OSC argument containing exactly 102 bytes.

Set JawOpen, byte index 36 counting from zero, to 255. Leave all other bytes at zero.

The avatar’s jaw opens. Keep sending the messages, but change JawOpen to zero. The mouth closes. Switching between these will make it open and close.

Actual result:

Native JawOpen controls the avatar’s mouth even though /avatar/avatarfullfacetracking reports false. Voice and Viseme both stay at zero.

Expected result:

I expected an avatar without full face tracking to retain its normal mouth behavior.

If this fallback is intentional, is there a way to disable it without disabling OSC?