Are you putting the call to the module in the "on view" bit of the card script? I've noticed there's times where it gets called twice for some reason when you transition to a card. I am not sure why or under what circumstances exactly, but I've been working around it by instead having it triggered by a button press (e.g. calling it in a "go to next card" button after the go[] function, rather than in the view function when the card loads) when I've needed it.
I think this is a decker quirk of how the view thing works rather than a thing specific to the typetext module, I've seen similar odd behaviour with other things I put in the view function.
You might be able to work around it in other ways (e.g. setting a flag that you check so it only plays the first time) but I'm not sure if that is causing more problems than it solves.