BUG: Flyouts not showing after WIN+L

[Royosef]

I'm using ModernWpfUI in my WPF app and recently I've encountered some pretty weird bug:
if you open a secondary window context menus (and all other flyouts) stop appearing after WIN+L .

I reproduced the issue in the ModernWpf.SampleApp by viewing the ContentDialog page and
clicking Open a new window:

clicking Show content dialog in this window:

and right clicking some of the text boxes:

after locking the computer (WIN+L) and reopening it the context menu stops from showing on right click:

[baochenw]

I also experience this issue. And I found this issue goes away when disable hardware acceleration.

[Royosef]

Unfortunately I don't have the option to disable it, is there any other solution for this? some change for the code?

[baochenw]

Disable Hardware rendering, using the DisableHWAcceleration registry value discussed in Disable Hardware Acceleration Option. This will affect all WPF applications on your machine; do this only as a way to test if your problem is related to graphics hardware or drivers. If that's the case, you can work around the problem by programmatically disabling hardware acceleration at a more granular level. This can be done on a per-window basis by using the HwndTarget.RenderMode property, or on a per-process basis by using the RenderOptions.ProcessRenderMode property.

https://docs.microsoft.com/en-us/troubleshoot/dotnet/framework/wpf-render-thread-failures#general-recommendations

[valves904]

Can confirm the following works to sidestep the issue:

<Window [...]
             Loaded="Window_Loaded"
             Unloaded="Window_Unloaded">

private void Window_Loaded(object sender, RoutedEventArgs e)
{
    // Force software rendering on this subwindow
    RenderOptions.ProcessRenderMode = RenderMode.SoftwareOnly;
}

private void Window_Unloaded(object sender, RoutedEventArgs e)
{
    RenderOptions.ProcessRenderMode = RenderMode.Default;
}

Not sure why this bug only happens on secondary windows however ¯\_(ツ)_/¯

[milos12345]

I have found possible reason for issues related to ModernWPF breaking after Lock/Unlock of workstation (in my case is ContextMenu breaking):
Having SystemParameters.DropShadowKey on auto and enabled on system, or enabled will cause this, so I can consistently break it if I start program with
Application.Current.Resources[SystemParameters.DropShadowKey] = true;
but it will consistently work after Win+L if I explicitly set
Application.Current.Resources[SystemParameters.DropShadowKey] = false;