I think I found the problem. I'm trying to do this for one of the built-in properties, and they seem to lack the PageDefinitionID which seems fair.
Is there still a way to determine what page type the control is being loaded for?
Edit: One way (a bit ugly) is to add a dummy property to the page type and look for this property.
You should be able to do;((PageBase)base.Page),CurrentPage.PageTypeID