WPF - Static Binding - Error shows up but everything works fine

Question

Hello Ok, I have a specific custom behavior for my MenuItems. So I bind the windows from my static class FormsResource and it works perfectly. But, very often, I get an exception "Exception has been thrown by the target of an invocation" in the 3 lines where I have "{Binding Source={x:Static local:foo}}" I can't see the inner exception, can't see anything, and when I run the project it runs fine. Here's my menu item code:

<MenuItem FontFamily="Segoe UI" Height="45" FontSize="16" FontWeight="Bold"
                      i:MenuItemWindowCallingBehavior.RegisterWindow="{Binding Source={x:Static local:FormsResource.cadcli}}"
                      i:MenuItemWindowCallingBehavior.AlterWindow="{Binding Source={x:Static local:FormsResource.altcli}}"
                      i:MenuItemWindowCallingBehavior.DeleteWindow="{Binding Source={x:Static local:FormsResource.exctcli}}"
                      i:MenuItemWindowCallingBehavior.MainWindow="{Binding ElementName=win}"
                      >
            <int:Interaction.Behaviors>
                <i:MenuItemWindowCallingBehavior />
            </int:Interaction.Behaviors>
            <MenuItem.Header>
                <Label Content="Cliente"  BorderThickness="0" BorderBrush="{x:Null}"/>
            </MenuItem.Header>
</MenuItem>

What's happening is it some kind of bug ?

Thanks in advance