refresh window in last portal row

I'm using comment's dwindling value list (in FMP 8.0), which uses the ValueListItems function and a script to refresh window [flush cached join results], in a portal. It functions perfectly except for one thing. If I'm creating a new record in the last portal row and enter information and then use this script (which is fired by button attached to the field being entered) the other information, the entire row or record in fact, disappears and I'm now selecting a value in a second new record.

Is there a way to not flush cached join results when in the last portal row?

And while on the subject of last portal row - is it possible to not tab into the last row when entering/changing info in rows above?

And