I am trying to:
Two things... one seems like a bug, the other is what I'm trying to accomplish.
The Bug:
I added the serial number filter to the filter control, it didn't work at all, so I deleted it. When I went to add it back in later, it was grey'd out, unselectable. This is the case for any filter I add and remove.
See Images "afterdelete.JPG" and "serialmissing.JPG".
What I'm trying to accomplish:
The serial number doesn't exist within the post (RETURNS) but instead within the related post (PRODUCT REGISTRATIONS).
See Image "serialnumberintemplate.JPG" and "relationshipfieldserialnumber.JPG" to see that I got this field to show up in the template.
Now I need to be able to filter by that field (serial number). But, as mentioned, I couldn't get the filter to work, so I deleted it from the filter box, and now I can't re-add it user the "New Filter" button to try different options.
Just to rephrase, I want to filter by this field that is contained with in a post type that is related to the post type for which the view is set.