AHAH Helper: Multiple submit causes form to blow up

This is a little odd. I don't even know where to look for the problem. Certainly nothing is coming up in the various log files.

I'm not sure if this is a bug report or a support request.

This is drupal 6 AHAH helper 6.x-2.2.

The setup and behavior I'm trying to create are specific to the use case and necessary.

I have 2 forms on a page. The first uses AHAH Helper. It's job in life is to collect parameters for the construction of the second form below it.

1) Adding and removing fields from the first form works fine.
2) Passing the collected values through the $_SESSION variable (in $_SESSION[form1_data]) works fine.
3) The configuration of the second form works fine.

So:
I submit form1 with one field. Fine.
I add a field to form1 and submit again. Fine.
I add a third field to form1 and submit again. The page explodes. I go to ahah_helper/params where I see raw JSON.

I'm pretty baffled by this behavior and would be grateful for any advice.

I should add that my actual Submit button has a #submit handler defined. Unlike my Add more or Remove buttons which have #ahah defined instead. I pass field values up into $_SESSION in that #submit handler.

Thanks for reading.