Originally Posted by gregbeal
There's another scenario (one among many variations):
Production company works with writer but finally gives up.
Writer sells the project elsewhere, and initial prod co reappears and threatens legal action if they aren't also attached to the project.
As I said, that's highly unlikely, but not impossible. The shadier the company the more likely it is, based on OP's description, the risk is probably not high. If he is really concerned about it, he can ask them for an agreement which states that any and all contributions made by them to any and all drafts developed during their discussions reverts to him should they decide not to continue with the project.