DateTimePicker: Calendar.SelectedDate not always updated and consistent

[lightwalker01]

Describe the bug
The Calendar part of the DateTimePicker component shows an inconsistent date if the user edit the date writing in the textbox.

To Reproduce
Steps to reproduce the behavior:

1. Select 01/01/2018 (european format) via the calendar popup
2. Close the calendar popup
3. Edit the selected date writing in the DateTimePicker textbox: 02/01/2018
4. Open the calendar popup
5. The calendar shows 01/01/2018 as selected date

Expected behavior
The calendar shows 02/01/2018 as selected date

Screenshots

Environment(please complete the following information):

• MahApps.Metro v1.6.5
• OS: Windows 10 Pro 1803
• Visual Studio 2017 15.7.4
• .NET Framework 4.7.1

[tymorrow]

I've also seen an issue similar to this when loading, via a DataTemplateSelector, a data template (as a StaticResource) with a DateTimePicker. The time selections in the picker get set properly with a new data context, and the date displayed in the text box is correct, but the selected date in the calendar is the last selection I made for a different data context. I'm making this comment just in case it helps you narrow down an underlying cause.