When you import using the Text Import wizard, the importtext statement is also used, exactly the same. However, there will also be a rearrange parameter added, which will depend on how you’ve set up the input template. But that shouldn’t affect whether records have tabs or returns in them.
If the CSV file is really “the same”, then you’ll get the same results. It’s the same code either way. If you can really get different results by importing a single file twice, with no changes to the file, I’d really like to see a copy of that CSV file. I don’t think that is possible. If you think you do have such an example and want to send me the file, I would also need to have the exact configuration you used for the Import Wizard field arrangement.