Hi Christian,
                  yes, we tested by setting MIXUPDATES = false and the error remains the same.

to reproduce it,
 
1) deploy a fresh basex instance from latest snapshot (BaseX80-20140519.172557.zip)
2) create an Empty database i.e. "sample"
3) Add the below function to the restxq.xqm

 declare  %rest:path("test1")
          %rest:POST("{$postbody}")
          %rest:consumes("application/xml")
  updating   function page:upd($postbody) {
         db:add("sample", document { $postbody } , "sample/dir1/doc1.xml")
};

4) now you can test the xml to the restxq url

url:                   http://localhost:8984/test1
content-type :  application/xml

<a b="1" c="2"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <b>
        <item x="1" w="2"/>
    </b>
    <n value="1" xsi:type="xs:string"/>
    <n value="2" xsi:type="xs:string"/>
</a>

or here is my complete basex instance which has only the above mentioned modifications : https://www.dropbox.com/s/yai9dx0smdj2ph9/test_basex.tar.gz

To be sure, i used the out-of-package configuration i.e. didn't modified any settings

Thanks,
Seenivasan

P.S : Platform: Linux
        OpenJDK 1.7.0_51

 
--

Seenivasan Gunabalan
Dedalus S.p.A
Via G. March 14/C, 57121 Livorno (Italy)
email: seenivasan.gunabalan@dedalus.eu