Unhandled exception occured while using DatePicker in Xamarin.Forms.ContentPage.

Hi,
I am trying to use datepicker control in in an application using Xamarin.Forms, but getting an error.
The first time the activity is started, date picker work just fine ... however, whenwe close the application via mobile back button and relaunch the app it throws an un-handled exception on opening date picker saying this exception:

    0x21 in System.Diagnostics.Debugger.Mono_UnhandledException_internal          C#

0x1 in System.Diagnostics.Debugger.Mono_UnhandledException C#
0x26 in object.56027ba0-2dd5-40f3-bfa1-daf5399d2134 C#
0x63 in Android.Runtime.JNIEnv.CallVoidMethod at /Users/builder/data/lanes/monodroid-mlion-monodroid-4.12-series/b5dc5ce9/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:490,138 C#
0x4E in Android.App.Dialog.Show at /Users/builder/data/lanes/monodroid-mlion-monodroid-4.12-series/b5dc5ce9/source/monodroid/src/Mono.Android/platforms/android-19/src/generated/Android.App.Dialog.cs:2497,5 C#
0x73 in Xamarin.Forms.Platform.Android.DatePickerRenderer.OnTextFieldClicked C#
0xB in Xamarin.Forms.Platform.Android.DatePickerRenderer.TextFieldClickHandler.OnClick C#
0x13 in Android.Views.View.IOnClickListenerInvoker.n_OnClick_Landroid_view_View_ at /Users/builder/data/lanes/monodroid-mlion-monodroid-4.12-series/b5dc5ce9/source/monodroid/src/Mono.Android/platforms/android-19/src/generated/Android.Views.View.cs:1840,1223 C#
0x17 in object.56027ba0-2dd5-40f3-bfa1-daf5399d2134 C#