This is old question and sorry that it is not documented well.

Set  reformatAfterEdit to true in the date field in colmodel like this:

Regards

I think I found an error in the way jqGrid is handling dates.

I have normal grid set up with the demogrid grid and date  like this

{name:'invdate',index:'invdate', width:80,editable:true,editoptions:{size:10}, formatter: 'date', formatoptions: { srcformat:'Y-m-d', newformat: 'd/m/Y'}},  The build of my invoice is ok . BTW ...the date is saved in database like 2014-02-18 but then showed as it should be 18/02/2014 .  I then use the navGrid option to fill in a new date .

In the before Show form I default a date like this

function beforeShowForm(formId)

var today = new Date();

var dd=today.getDate();

var mm= totday.getMonth()+1;

var yyyy=today.getFullYear();

if (dd<10){

dd='0"+dd;}

if (mm<10){

mm='0'+mm;}

today = dd+'/'+mm+'/'+yyyy;

$(#invdate",formId).val(today);

this gives me todays value into the input screen .

In the data send via json it goes in the form 18/02/2014 which is so far so good.

(naturally I convert it to the used format 2014-02-18 before entering in the database .

When I auto redraw the grid things go ok .

BUT 

when I don't do anything with the postdata(and leave it to the default way) the entered data is wrong in the grid .

I have now (as a work arround ) altered the postdata back into the form 2004-02-18 (in the aftersubmit procedure) before leaving it up to the grid logic to display the new row . This goes ok but without 'aftersave' conversion its wrong .

Thanks