Since the change to using the spout library for exporting csv files the file encoding has changed from utf-8 to utf-8 + BOM (Byte order mask).

The difference here is that Excel has greater trouble opening and then saving the utf-8 + BOM files and the resulting file ends up being a tab separated file. By default we use commas as the separator and the user needs to know that their file is now being separated by tabs.

Fred's comments about this problem:

I thought of a few ways to fix the usability regression:

1. Try to guess that the delimiter has changed from what it was supposed to be. We know the columns, and we know that they were meant to use commas.
   • Cons: This only fixes assignfeedback_offline, and can be unreliable
2. We force dataformat_csv to never include the BOM, that would match our home made exporter behaviour but I'm not sure of the consequences.
   • https://github.com/box/spout/blob/master/src/Spout/Writer/CSV/Writer.php#L66
3. We change assignfeedback_offline to use or home made CSV exporter.
   • Feels like a step back...

Perhaps option one is the best way to proceed.