LibreOffice is saving CSV files with tabs as separators
For some users (thoses using KDE), the "edit filter settings" box is gray. A workaround is to use Openoffice dialogs. Tools > Options > LibreOffice > General > Open/Save dialogs > Use LibreOffice dialogs
Then you will be able to choose the field delimiter wanted.
That bug was reported here : https://bugs.freedesktop.org/show_bug.cgi?id=72187
When you export a CSV file, go to File > Save As, select Text CSV as file type and then go to Edit filter settings.
In this dialog you can select the cell delimiter and change it from Tab to a comma.