This is the clue:
"If I 'Refresh Window' the portal is then refreshed showing the correctly filtered items."
By definition, a filtered portal is based on an unstored calculation. Unstored calculations do not refresh until the object or window containing them is refreshed.
Thanks for the feedback Mike,
However I'm not certain how this applies. I employ that same script on several other layouts and the filtering works as expected.
I also removed the portals from the parent container (the popover) and placed them directly on the layouts in question and they also worked as expected.
If 'refresh' is the issues, i'm still somewhat confused.
I suggest you add a Refresh Object script step to your routine (name the portal if necessary) and see if that doesn't solve it.
I did actually consider that but thought I would post here first as it seemed like 'buggy' behavior.
It's not. It's normal.