I don't know if this is an actual error or there is a technical reason behind it, but wouldn't it be better to return "other" in this case?
Update: There are several file types that also returns "doc" (e.g. txt, xml, etc) as their metadata type, althought they can't have any property of this type (category, author, etc).
The properties item.metadata.doc.doccreateddate and item.metadata.doc.doclastsaveddate can contain data.
I don't think the value of item.metadata represents a limit on the type of metadata (as an object) that can be accessed.
e.g. An exe file who shows item.metadata as "exe", but you can still get their copyright value via item.metadata.doc.copyright
It seems like the OS now returns a couple of metadata property fields for all files/folders (created / last saved) which I'm pretty sure didn't used to happen. We'll change it so those fields are ignored when determining whether a file has primarily "document"-type info.