You never know, you could have the world's most poorly written stock vesting contract, but it seems very unlikely that their vesting scheme was designed so that vesting didn't matter in the one case where vesting actually does matter. You don't need a "forfeiture" clause for vesting to have teeth. You'd probably need to share more of the details for us to noodle around any further with this.

(If you've got any kind of confidentiality agreement with your former employer, don't share details.)