Take a look:
I defer to the experts, but Wagner as part of “Production” seems off to me. Perhaps better classified as a Composer of sorts?
John,
You can see all roon’s credit role assignments in the KB:
https://kb.roonlabs.com/Credit_Roles
As you can see a Librettist is indeed a “Production” role:
On the other hand, rather inconsistently IMHO, lyricists and poets do get assigned a “Composer” role.
For this reason, many modern “productions” of Shostokovich Symphony No. 13 'Babi Yar" give a rather confusing composer credit to Yevgeny Yevtushenko whose poetry is read in some performances.
BTW, Wagner was routinely also a librettist on his operas. This was/is unusual, so your choice of case complicates finding a better rule for roon to handle these scenarios.
I did a quick check in my library and I find that Wagner gets a Production credit on 22 of my albums. All for being a librettist. Paradoxically this is the easiest way in roon I have of finding Wagner albums as roon’s default focus for composers is compositions. 
In other cases I just delete any composer Production credits as I am not interested in them and I would prefer simpler screens. In fact, I would like to be able to globally delete “Quotation Author” or better to toggle production credits on/off.
So clearly these role assignments have knock on effects on search and presentation. My concern would be if it is also having an effect on background queue construction processes like radio. But it is certainly the reason why when you do a search on a composer you will usually see confusing duplicate and/or sections of main, performer and production “albums” presented. Another annoying and inconsistent one is a composer can be rather arbitrarily assigned an “orchestration” or an “orchestrator” role. In these cases roon will treat Orchestration as “Production” but Orchestrator as “Composer”.
You can delete and/or change these credits if you don’t like the role assignments. But of course it is a lot of work. I don’t know if these role assignments are set in stone or there is a reason they are as they are or there is scope for roon to change them or scope for users to maintain their own custom tables of role assignments.
However, if you browse through the link above I am sure you will find a lot of assignments that don’t seem to make much sense or are contradictory.
Thanks for the additional info Tony. Unless these categorizations came from the IOCCA (International Organizing Committee for Category Assignments), we can petition for reassignment. Wagner doing something, anything with Production (of the performance or CD) just seems wrong.
But what do I no? [sic]
I have the same feeling that in many cases the results displayed on screen just seem “wrong”. I find myself more and more performing a secondary re-tag of these sorts of things and also other tags to force composition level level identification in identified albums. Most of the time I seem to be performing repeatable edits. So there must be scope for more automation from roon or more toggles related to composers and compositions so that displays are more configurable to personal tastes.
You hope that the roon changes the credit role assignment for librettist to composer - because that’s where it would belong (I mean: lyrics are treated as part of compositions so …). The credit role assignment has a 
bug here… … you could try calling support. 
As a workaround you might change librettist to lyricist. It’s a closer match if roon insists that the model is right the way it is.
okay, I’ll try the bug report route again. Thanks for the nudge.
Yeah, this is a bug. We will move Librettist to the Composer category.