API Rest json vs xml

I have a problem with API Rest and the request XML or Json.

For Example:

JSON Resquest :

curl "http://.be/helpdesk/WebObjects/Helpdesk.woa/ra/Clients/1506?apikey=XXxxXX"

{"id":1506,"type":"Client","email":"IT@.be","firstName":"IT ( "lastName":")","notes":null,"phone":null,"phone2":null,"department":null,"location":null,"room":null,"username":"IT","companyName":null}

It's OK

XML request :
curl "http://.be/helpdesk/WebObjects/Helpdesk.woa/ra/Clients.xml/1506?apikey=XXxxXX"

[{"id":1962,"type":"Client","email":"

XXXXXX

"firstName":"IT ( "lastName":")","notes":null,"phone":null,"phone2":null,"department":null,"location":null,"room":null,"username":"IT","companyName
":null}]

it's not the same response.

XML Request with qualifier:

curl "http://.be/helpdesk/WebObjects/Helpdesk.woa/ra/Clients.xml?qualifier=(email%20like%20'IT)&apikey=XXxxXX"

  <?xml version="1.0" encoding="UTF-8"?>
<Clients type="Client">
<Client id="1506" type="Client">
<email>IT@.be</email>
<firstName>IT ( </firstName>
<lastName>)</lastName>
<notes nil="true"/>
<phone nil="true"/>
<phone2 nil="true"/>
<department nil="true"/>
<location nil="true"/>
<room nil="true"/>
<username>IT</username>
<companyName nil="true"/>
</Client>
</Clients>

it's ok.

what's happened?
my request are not correct?

thank's you for your help