Can anyone else confirm that they have an issue with the following?

Create a simple file in Excel:

- One column file

- Column A heading: Email Address

- Column A values: enter your email and a test email (perhaps a colleague)

- Save as type "CSV (Comma delimited) (*.csv)"

Open your Sandbox instance, attempt to upload the file into a list.

I am getting an error when attempting to do this (as well as explicit UTF-8 format save) that states "Invalid file type 'application/json'; must be CSV, semicolon, or tab-delimited text file".

I am getting an error upon this attempt and Support, while making a valiant effort to help has not been able to provide a sufficient answer IMO.

The response I received does not speak to the issue or underlying cause: "There are some subtle differences between the sandbox and production instances as the sandbox instance is designed for testing. From the screenshots you provided, the import is set to auto-detect the file. I would change the file format to comma separated values. It is not seeing that the csv format on this file."

IMHO (and my latest response to support since opening on 7/29/2016): "Something must have changed since just before I entered this ticket. I was able to upload CSV files without explicitly selecting format prior to this change. There must be a changelog for the codebase to trace back to what may have changed! And, while I understand that Sandbox is designed for testing, it should not be technically different in any way than Production to ensure a true test prior to Production deployment. This is simply common practice!"

First, I always select CSV because I don't trust the UI.

Second, I have had occasional problems with lists when bad characters get into Marketo or there are protected fields that we were unaware of. I have been able to push Support to dig into this sort of thing, but it took a month. Most of the time it is a character or SFDC issue.