Saxon

What's happening in this case is that validateAttributes() is being called twice. The "standard" call is from the ContentValidator handling the specific complex type, but because the element has assertions, a second call is being made, as part of the process of building the tree used for assertion testing. Because of the structure of the validation pipeline, it may be difficult to avoid validating the attributes twice, but perhaps the second call can be done silently, without generating additional error messages.