getFormData converts calendar's input value

I have form with 2 calendars:

{ type:"calendar" , name:"data_zaw", label:"Data rozpoczęcia", required: true, dateFormat:"%Y-%m-%d", serverDateFormat: "%Y-%m-%d" }, { type:"calendar" , name:"data_odw", label:"Data zakończenia", required: true, disabled: true, dateFormat:"%Y-%m-%d", serverDateFormat: "%Y-%m-%d" },

When I fill it in via myForm.load function with dates like 2016-12-01 and 2016-12-31 and I will execute form.getFormData I will receive the corresponding dates:
2016-11-30T23:00:00.000Z
2016-12-30T23:00:00.000Z

those will be saved to database as 2016-11-30 and 2016-12-30 which is completely wrong. How can I fix it?

Hi

try myForm.getFormData(true)