When a part or assembly is added to a workspace on the fly (on demand), the format is not included, even though it is required by the drawing. This happens even if the default collection preference is set to "Required".
These collection preferences are being ignored for on-the-fly retrieval of files by Creo. This behavior leads to ghost objects being created in the workspace anytime a part or assembly is duplicated in Creo without first adding the format to the workspace. It also makes it nearly impossible to use Creo part (or assembly) templates with a drawing already associated to them since every time you use one another ghost object is created.
The workaround is to either manually add the required format to the workspace in advance, or manually open the drawing in Creo (so it will pull the required format) before duplicating the part (or assembly).
Windchill is obviously smart enough to know the drawing has a dependency on the format (hence the creation of the ghost object). It should be smart enough to automatically add the missing format to the workspace on the fly (just like it does for any other Creo dependency.)