Description:
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Changes made in libxml2 between version 2.6.23 and 2.6.24, exactly rev. 1.366 of tree.c, exactly added return(NULL) in xmlSetProp(), cause attributes with unknown namespaces to be silently dropped, instead of added into the document.

PHP SOAP extension, when making a client request, when running in "encoded" mode, is adding xsi:type attributes to nodes (soap.c line 3948). The xmlns:xsi namespace is added later in that function (soap.c line 4073).

Paired with the behaviour of a new libxml2 release, this leads to the xsi:type attribute not being added.

Possible solution is to move if (use == ENCODED) block above the for (i = 0; i < arg_count; i++) block in serialize_function_call() in soap.c.

Reproduce code:
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$client = new SoapClient("https://oas.hide.vol.cz:4444/WS-NPLAN-context-root/WS_NPLAN?WSDL", array("trace"=>true));
$client->getProfil(4);

Expected result:
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... <ns1:getprofil><profil xsi:type="xsd:decimal">4</profil></ns1:getprofil> ...

Actual result:
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... <ns1:getprofil><profil>4</profil></ns1:getprofil> ...