Canceling Mulit-line tag causes issues

I tested the use of a multi-line tags by changing my user created albumartist field (labeled narrator for audiobooks) to multi line with the tick box (Options/Tag Panel). As the multiple artists(narrators) wouldn't show uo in itunes I unticked this field. Though the field in mp3tag no longer shows multiple lines in the input box the actions I have created including renaming of the folder to include the narrator in the folder name and the albumartist field in my export text have ceased working.
Folder rename action omits that field and the export text breaks the multiple narrators into multiple lines.
Is this a bug or am I able to correct this myself?
I have tried:
Deleting the tag fields and recreating them
upgrading from V2.59 to 2.61a

NOTE: This error is duplicated with the subtitle field I used to experiment at the same time.
Regards

To get several lines, you have to insert the characters for "carriage return" and "line feed" (this is very basic DOS stuff which dates back to the times when computer output was mainly on printers).
These characters are invisible as they serve that particular function.
So: if you export such a field, you get either the result you have just experienced - the control characters in the middle of a record and therefore unusable output for csv files as the "line break" is also teh "end-of-record" marker.

What you should do: replace all $char(13)$char(10) sequences in ARTIST with something that does not lead to a line break, e.g. "; "

For an export you can define in the export script that during the export every $char(13)$char(10) sequence is replaced with something visible, e.g. the # which you can easily replace with linebreaks in the target application.
e.g. $replace(%artist%,$char(13)$char(10),#) instead of the plain %artist%

One further note: the representation of data in MP3tag hardly ever changes the contents of a field. So switching between multiline and no multiline does not get rid of the linebreak characters

I see. The line break is being remembered in the tag not in mp3tag. I was able to delete the tag in the mp3's and rewrite them which I guess is essentially what you were saying. Thanks again for your help in directing my understanding of how things work.

You can replace the invisible control characters 13 and 10 with something visible. You do not have to delete the rest and rewrite it.

As it was an experiment I only used the multi-line tags on 2 folders totalling around 40 files so it was easy just to replace the 2 tags which were all identical within the files of each folder.

Are you sure, you have not confused "multi-line" and "multi-value"?

DD.20140710.1240.CEST

The option I am talking about is in Tools - Options - Tag Panel - Add Field - at the bottom there is a tick box for multiline

multi values would be great but they can't be read by itunes as far as I can figure out