I wouldn't recommend a setup like this. I'm not saying it won't work in certain instances, but params are best set with default values in the Designer, and those values can be overridden when the View is opened via whatever mechanism you're using (in this case the Popup Action or openPopup() ).
So if you're setting the param in a startup event, you might never see that value if it's overridden by an Action/Script.
All of that being said, I was able to replicate what you're seeing and we definitely do NOT want that param view to reset itself. I'll open a ticket to get it fixed.