This should work for you without any special handling. Since it doesn't, you'll need to take a closer look at your layout where you use your portal to do this and see what's been set up differently. I'd check to make sure that I'm specifing the exact same value list for both layouts.
I've checked, and the lists are the same.
The same fields and value lists are used on both layouts, the behavior should be the same as well.
Is this value list a conditional value list?
Are all of these tables and layouts in one file or is there more than one file involved?
Could you upload a clone (empty copy) of the file to a share site and post the link here so someone can download it and look at it?