[DanCooper]

I have tried it with a movie. The initial .nfo file was:

Code:

<id>tt1038988</id>
<uniqueid type="imdb">tt1038988</uniqueid>
<uniqueid type="tmdb" default="true">8329</uniqueid>

and when I have exported it again from the Library it became:

Code:

<id>8329</id>
<uniqueid type="imdb">tt1038988</uniqueid>
<uniqueid type="tmdb" default="true">8329</uniqueid>

Does it make sense for you? I'm quite ignorant...

And the field <id> is added even to TV Show and Episode .nfos.

Yes, but me question is: how is the ordering of multiple IDs for one movie in the table uniqueid? Will the "default=true" value always added as first entry in the table?

Being ignorant...what do you mean by table uniqueid? Should I take a look into the Kodi database?

Yes ! :-)
There is a table called uniqueid. All IDs are saved in this table and linked to movies/tvshows/episode tables. There are no longer single field in tables movies/tvshows/episodes for an ID.