registering viewmodel as singleton does not work

[stevensrf11]

I registered a viewmodel and its interface as a singleton as shown
containerRegistry.RegisterSingleton<IXPubEntStatusBarWindowViewModel, StatusBarWindowViewModel>()
In code a int property on the interface is set to a value of 2.
The later when the interface is dependency injection into a constructor that property is not to 2 it is set to the default value.
How come that happens