Android :: AlertDialog.show Silently Ignored Within Service

I have a service running a background thread. What I'd like to do is to show an AlertDialog initiated from my background thread. I know that this is not the recommended way of notifying the user and that it interrupts the workflow (as they can pop-up in any application at any time) but it's a suitable way for my use case. There is a handler registered with the background thread and showing a Toast notification withing the handler works fine. But after switching to an AlertDialog nothing happens anymore. My showDialog logic is silently ignored. No Dialog window appears, no log entry. It's a bit strange as I'd expect at least a log entry saying that I'm doing something wrong or whatever. Are there any limitations for showing an AlertDialog initiated from a service background thread? Some people seem to recommend a Dialog themed Activity to get a similar behavior.