Is this behavior happening in all the browsers?
Basically the value of the DateTimePicker should be persisted. Check the following demo:
I assume that you have specified default value
and because of this the state is lost (I can see that you have specified value through the Value method). It all normal since the scripts are re-executed, this is the default browser behavior.
Regarding the Grid - probably the same is happening - the value of the DateTimePickers is changed to the default one and the default values are sent to the server.
Consider removing the default values if you want to avoid such behavior.
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