IDialogService ShowDialog - blocking execution in calling module

[JoeSenDev]

I've implemented a custom modal Progress dialog for a multi-module WPF Prism application using IDialogService. The dialog itself is opened, updated, and closed using a helper class held in my infrastructure module using the ShowDialog method.. My issue is that when I instantiate the helper class from the MainWindowViewModel all works as expected. but if I instantiate the helper class from another module's ViewModel and try to open the dialog then execution in that module is blocked. If I change the' ShowDialog' call to 'Show' everything works as expected.

Is this the expected behaviour? If so, is there a work-around? If not, am I doing something incorrectly?