ExtJS: Date field writes the date one day back? - date

Question

I'm using a 'Ext.form.field.Date' and on CRUD process it writes given date as one day back. I mean if I select 05 June 2018, it writes as 04 June 2018.
I've checked related model and widget itself but nothing seems weird! Why this could be?
Here is model statement and field;
Ext.define('MyApp.FooModel', {
extend: 'Ext.data.Model',
fields: [
{name: 'mydatefld', type: 'date', dateReadFormat: 'c', dateWriteFormat: 'Y-m-d'},
//and implementation
Ext.define('MyApp.BaseDateFld', {
extend: 'Ext.form.field.Date',
xtype: 'basedatefld',
format: 'd.m.Y',
flex: 1,
labelAlign: 'right',
name: 'MyDate Fld',
fieldLabel: 'MyDate Fld',
bind: '{currRec.mydatefld}'
});
Each time saves date as on XHR request payload;
2018-06-05T21:00:00.000Z //But should be 2018-06-06T06:05:00.000Z
Update:
I've tried change dateWriteForm to 'Y-m-d H:i:s' and 'Y-m-d H:i' but still noting changes on payload and keep decrease one day and sets time to 21:00:00
As well tried to change compouter TS to some another as #Alexander adviced but nothing changed.
Update 2:
I've over come the current issue but really a very DRY solution, so not safe!
Below there is insertion method (update method is almost same as this) and formating the related date value on here, thusly became success.
Server accepting the date format for this field as Y-m-d, so I've stated dateWriteFormat on model and submitFormat on datefield as 'Y-m-d' but it keeps write the date value with timestamp.
When I check rec param on method it is as 2018-06-06T21:00:00.000Z(The TZ part shouldn't be here!). And store param changes the givin date one day off as 2018-06-05T21:00:00.000Z.
Still not sure why I can't convert/format through model or field.
Thanks for advices.
recInsertion: function (rec, store) {
store.getProxy().url = store.getProxy().api.create;
rec.data.givindate = Ext.Date.format(rec.data.mydate, 'Y-m-d'); //This is current solution to format date! Which is really not safe and will cause DRY.
Ext.Ajax.request({
url: store.proxy.url,
method: 'POST',
jsonData: JSON.stringify(rec.data),
callback: function (options, success, response) {
Ext.GlobalEvents.fireEvent('showspinner');
if (success) {
Ext.GlobalEvents.fireEvent('refreshList');
}
else
Ext.GlobalEvents.fireEvent('savefailed');
}
});
},