Sorry for the delayed response. :)
That's pretty crazy looking, I'm trying to replicate it but can't seem to get the jaw to do that with base G8F and the expression, with a fresh "locked" character or with one that's been "easy unlocker"-d.
I've tried applying the expression without unlocking, with unlocking, also with the separate jaw unlocker from the BJ sets, I can't get anything like that to happen at all.
I really want to help you with this (and I love hunting down wierd things like this). Can you please replicate the pose, save a scene file of it (with the expression active) and then email a copy of the scene file to me at the email address in the readme?
I have a feeling it may be either a character morph or morph kit that is not playing nice with the pose, or another expression set that contains custom morphs that are activating by accident.
Question:
Is this happening on all the lower expressions or just that particular one?
All my expressions are built from the core DAZ sliders, so no extra morphs should be activating, I'm very curious to see what's causing this. :)