I give...I am hoping someone has a good answer.
I create a content type based on a Document Set (called A). I create a document library and allow this new custom content type to be added to the library. I add one column (say Car Phone) to the new content type(A).
However, if I do anything to the editform.aspx through SharePoint designer it completely ignores any custom fields on my content type A. Now, when selecting the item, and selecting edit i do not see my Car Phone Property. This occurs only when i do anything to the editform.aspx that exists in the document library. Just copying to a new name and setting as the default edit form it ignores my custom properties on the content type A>