OK so I couldn’t come up with a concise post title that describes the problem!
I was writing XML to deploy a number of custom fields through a feature. The feature activated fine. Two of the three fields were visible in the Site Columns gallery. The 3rd just wasn’t there!
It turns out because I forgot to have the DisplayName attribute in my <Field> XML! There was no error messages whatsoever! Thanks a lot SharePoint! >:[
And another thing that bugs me is Field vs Column. In everyday speak – what should I be using to refer to custom Field/Column? (I finally got my head around Site vs Web!!)