Hi Stephen,
I created a similar form sometime back, where the subtype of a feature class was selected on one page, which changed the available options for the comboboxes on other pages and had multiple comboboxes tied to one attribute. The only work around I ever found for the same problem (not saving anything) was to populate the combo boxes' options with an SQL query (it was an AXF) and not have any of the comboboxes tied to the attribute itself.
You have to then add code to save the attribute manually during the form "unload" event. Something like:
Determine which combobox you want to save based on blankness
Get a reference to the fields
field.value = combobox.value
Nothing too fancy, but still a hassle when it seems like this (if the user has multiple comboboxes tied to the same attribute, use the value of the populated one) should be part of ArcPad's logic.
Hope this helps,
Eric