See the link to the issue origin thread.

1. Ensure that the topbar is not disabled in myTVFullScreen.xml

2. Start TV, go to fullscreen and move your mouse to the top of the screen. The topbar will appear.

3. Hit the channel up button on your remote to change channel.

4. Move your mouse to the top of the screen again. This time the topbar does not appear.

Just to be clear, although this was reported in a thread related to another issue, this problem was not introduced during fixing of that issue. It is present in plain 1.2.0beta, and probably earlier.