jQuery Grid Plugin - jqGrid

I'm using utf-8 in my application and all data are correctly displayed in grig.

    ajaxGridOptions: { contentType: 'application/json; charset=utf-8' }

....

If I define searchoption as la list of values:

{name:'office', index:'office', width:50,  search:true, stype:'select', searchoptions:{ value: ':All;Uff. Contabilità Generale:Uff. Contabilità Generale'}}  

all works fine.

If grid reads values form URL:

{name:'office', index:'office', width:50,  search:true, stype:'select', searchoptions:{ dataUrl: 'QueryField.do?v=office'}}

the server send the string:

<select><option value=''>All</option><option value='Uff. Contabilità Generale'>Uff. Contabilità Generale</option></select>

but inside the combo box the string is diplayed with a question mark over a black square  instead of 'à' and search hangs.

What am I doing wrong ...?

Thanks