As title suggests, I had a site column defined in the xml of a content type.
The site column was required. I have just changed the definition of this field (it is not defined anywhere else in the solution) so that required = false.
Under 'Site Columns' of the Site Settings page, I can see this change has been implemented as I'd expect.
However, on the Site Content Type it still appears as a mandatory field. Is it not possible to push this change out to all content types that reference the column? This will need to be done on several environments so as you can expect I need it to be as 'automated' as possible. Deleting the content type is not an option.
NOTE: I did remove the site column manually from the content type and re-added it, it is now optional. As I say though, that's a far from ideal approach.