Dynamic picklist clears at start of action

Dynamic picklist clears at start of action

Hi -

I'm trying to build a dynamic picklist from the selections in another dynamic picklist using a custom button on a stateless form.  Here's the scenario:

1.  Picklist1 is populated based on the selections in other fields.  (Works great)
2.  User selects entries in Picklist1 then clicks on Add button to add entries to Picklist2.  (Works the first time)
3.  User can then change entries in Picklist1.  (Works great)
4.  User selects entries in Picklist1 then clicks on Add button to append entries to Picklist2.  (Doesn't append; instead replaces previous entries in Picklist2)

It seems that Picklist2 is being cleared at the start of the Add->On Click action.  I don't have a Clear statement in the script.

I tried a workaround of using selectall() on Picklist2 at the start of Add->On Click then saving all the current entries to a temporary list variable and readding them to Picklist2.  However, selectall() is not supported in the On Click action.

Any suggestions on how to implement this functionality would be very much appreciated.  Thanks.