Right now, Voice Commands registered for an app only work when an app is off, or in the background. They do not work if you are in the application already, and use Speech from the Windows key to navigate somewhere else in the app.

To the end user, it appears that the command is recognized and the system is taking you there, then it closes without actually doing anything. This appears to the end user like a bug in my application, not a system-wide OS bug.

I understand this was not necessarily the designed use case, but consider that the search button takes you back to the main Bing search page, no matter what part of the Bing app you are in... the hardware buttons need to work consistently for the sake of the end user, even in use-cases you didn't originally intend.