I am sorry to hear you are experiencing this issue.
From your explanation it seems more like unexpected dialog rather than OpenFileDialog. Could you please try to use this code instead:
this.Manager.Settings.UnexpectedDialogAction = UnexpectedDialogAction.HandleAndContinue;
If you continue experiencing this issue please provide more information like screen shots or short video demonstrating this behavior. The best scenario here will be if you can provide us with access to the application you are testing so we can take a look.
the Telerik team