482KB sounds about right. After it's complete, it should popup a dialog to ask you, if you want to email the output?You never got that? Do you mind retrying the export after a fresh reboot and letting me know about the behaviour?
The only thing that comes to me is that, maybe you had other apps running already consuming enough memory and leaving txtract no room to process?
I cannot simulate the full load on the simulator, so I need to do a live test on my phone, and I don't want to solicit all my friends with a ton of messages the same day

In a few days, I'll try to bump up my message count to those levels and debug the app again.
Thank you very much for letting us know about this problem.