An assembly can map one CLR namespace to several XML namespaces: PresentationFramework
maps its namespaces to both the winfx/2006 and the netfx/2007 presentation namespace. The
fallback used when the BAML xmlns records name no namespace for a type always preferred the
winfx/2006 one, so a document that binds the default prefix to netfx/2007 ended up with a
root start tag that declares one presentation namespace and needs the other for its own
name, which XmlWriter rejects. Only the root carries the xmlns declaration, which is why
skipping XClassRewritePass worked around it.
Assisted-by: Claude:claude-opus-5:Claude Code
Siegfried Pammer