Well, that's really weird ...
I just tested it again from my iPad and the custom fields maintained their set values when I selected EDIT function on an existing ad. They didn't revert to a default status as if nothing had yet been selected, as they did when I tested it with Firefox 3.6.4 last night.
I then logged into Firefox 3.6.4 and sure enough, they seemed fine today.
I wonder if this is another one of those anomalies that can be attributed to Firefox (and Safari) on the MacBook Pro under OSX 10.6.4 that we've chatted about before. The last one I still have the "last x" display problem where ALL ads appear whether I select last day, last 7 days etc.
I suspect there's something about the way the cache is used on the Mac with browsers that is causing these strange behaviors. Does that make any sense?