Error XTDE0485 reads:

[ERR XTDE0485] It is a non-recoverable dynamic error if namespace fixup is performed on an element that contains among the typed values of the element and its attributes two values of type xs:QName or xs:NOTATION containing conflicting namespace prefixes, that is, two values that use the same prefix to refer to different namespace URIs.

I haven't succeeded in writing a test case for this error, and I'm coming to the conclusion that it can't happen. The reasons are actually explained in the Note immediately preceding the error description:

(a) Namespace fixup happens before validation, so you can't create xs:QName attributes and then do fixup on them.

(b) You can't copy namespace-sensitive attributes to a new element while preserving the type annotation, because there is no mechanism to keep the namespace context the same.

I'd be interested if anyone can produce a use case showing how this error can happen.