It's important to reference the latest spec. The language is a little bit different:


    A client MUST submit a Depth header with a value of "0", "1", or
    "infinity" with a PROPFIND request.  Servers MUST support "0" and "1"
    depth requests on WebDAV-compliant resources and SHOULD support
    "infinity" requests.  In practice, support for infinite-depth
    requests MAY be disabled, due to the performance and security
    concerns associated with this behavior.  Servers SHOULD treat a
    request without a Depth header as if a "Depth: infinity" header was
    included.

So I guess the correct thing to do is actually return an error when somebody requests an infinity propfind and we're not willing to accept that. I'm a bit worried that this would cause other clients to break though.