I have this chronic, recurring issue with list uploads that's, well, irritating me off at this point.
Why does this happen?
The list that I've uploaded never had address in it in the first place. The fields appear to be right but this happens probably on 50% of my uploads and I have no idea what causes it. Can you just improve list uploading entirely, please? If I have CITY, it breaks the entire upload because of... caps. Yep, caps affects this stuff.
Also if I change a single field in the list upload, it removes every other field entirely, meaning I have to edit the spreadsheet, save it and try again. Seriously?? (I should ask though, is this a feature or a bug? I'm never sure!)
These are net new leads as well.
What you are seeing in the screen shot is basically a behaviour Marketo uses when you run multiple list imports. You may not have an address field in this current list, but you may have had it in a previous list in where you attempted to map a "blank column name" to "address". Marketo tries to identify that and apply that on your next list upload. Also from the looks of the screen shot, while there may not be a sample value shown, if you go back to the list that you are trying to import, can you see if there are additional columns where there is data? If there is data in that column but no column name, then Marketo is just attempting to do what would have been done before that is a map the blank column name to Address.
You have to ensure that your list column names which are on the top row of your list match what Marketo accepts as a default. If you are going to change a field name, Marketo assumes that all the other column names have changed and looses the behavioural mapping.
Now you can set your own list import alias for each field in Marketo. You would need to go to Admin->Field Management->"Select the field you want"->Field Actions->Edit List Import Alias. That should help you define a structure when you are trying to do a list import.
Hope this helps