Validation-Popup won't be opened after closing by mouse left button down

[andy294]

What steps will reproduce this issue?

• Open MahApps.Metro.Demo.Shared\App.xaml
• Change the Property 'CloseOnMouseLeftButtonDown' of the 'MetroValidationPopup'-Style to 'true'
• Start the MahApps-Metro-Demo-Application
• Open the 'text'-Examples-View
• Go to the TextBox with the watermark 'Number smaller than 10' and enter a number smaller than 10 (The validation popup is visible)
• Click with the left mouse button on the validation popup (the popup will be closed)

Now it's not possible to open the validation popup again.

Expected outcome

After closing the validation popup by mouse left button down, the popup should be opened, when the TextBox will be selected again.

Environment

• MahApps.Metro v1.4.3
• Windows OS 7
• Visual Studio 2015
• .NET Framework 4.6.2