I assume we are talking about mp3s here.
The Genre field (TCON frame) store values null separated.
The Grouping field (TIT1 frame) stores values comma separated.
When displayed in Jaikoz, null separated fields are interpreted as multiple values but commas are not specially separated so just shown as one value.
There isn’t an option to change the behaviour because the grouping field is meant to be like this however it is easy to change fields from comma separated to null separated in Jaikoz.
Select all fields in Grouping column.
Right click and select Edit/Find and Replace
In Find field enter ‘,’ (don’t include the apostrophes)
In Replace field enter ‘\u000’ (don’t include apostrophes this is unicode for null)
Set Columns to Grouping
Select Replace All
They are now converted, if you reopen the files in Jaikoz only the first value will now be shown in the grouping field because now null separated and the Jaikoz UI does not support showing multi values in the grouping field. But if you open the files in Foobar you’ll see all values are preserved.