Hi Dave,
>> On a browse, after upgrading to 4.31 a Unique,unchanging key field became blank.
I'm not 100% sure about this. As far as I can tell it's not that it makes it blank, it's more that it suddenly, absolutely, requires it to be filled in. In earlier versions if it was blank it used the Key set under the "tables" button, and failing that used the file's primary key.
In 4.31 though, I've made it stricter - the uniquekey _must_ be set.
Cheers
Bruce