Steps to reproduce:

1. create dashboard with widget hidden header (view_mode = 1)

   {
       "name": "dashboard",
       "widgets": [{"type": "clock", "view_mode": 1}]
   } 

   "dashboardids": [
       "12"
   ]

2. get this dashboard

   {
       "output": ["dashboardid", "name"],
       "selectWidgets": ["widgetid", "type", "view_mode"],
       "dashboardids": 12
   }

   {
       "dashboardid": "12",
       "name": "dashboard",
       "widgets": [{
           "widgetid": "17",
           "type": "clock",
           "view_mode": "1"
       }]
   }

3. update this dashboard with minimum specified fields

   {
       "dashboardid": 12,
       "widgets": [{"widgetid": 17}]
   }

   "dashboardids": [
       "12"
   ]

4. get this dashboard again

   {
       "output": ["dashboardid", "name"],
       "selectWidgets": ["widgetid", "type", "view_mode"],
       "dashboardids": 12
   }

   {
       "dashboardid": "12",
       "name": "dashboard",
       "widgets": [{
           "widgetid": "17",
           "type": "clock",
           "view_mode": "0"
       }]
   }

Result:
"view_mode" field resets to default value
Expected:
this field should be unchanged