We have a bit of debate at my office regarding the new 38.04.

The code says that the offense is a state jail if the actor had previously been convicted under 38.04.

So, does the prior 38.04 conviction have to be after 9/1/09 or can it be before 9/1/09 to trigger the state jail enhancement?

I don't think the timing of the prior conviction matters unless the statute expressly says otherwise. It would not be an ex post facto law so long as the conduct that gives rise to the current offense occurs after 9/1/09 since the new offense is the one being punished.