So as I understand the thread comments here, the "undocumented feature" is actually rather useful and as Kevin says nice to have music through the HiFi and video through the TV. It does it automagically if you de-select MMAL
The add-on linked above will not work with the Slice if I understand Gordon correctly.
Therefore to keep the feature, please can you developer chappies avoid fixing the "bug" or requesting others to fix it.
For me it is great and what I have been looking for since I started using the Slice for video as well as music.
If it has to be fixed or is broken by other means, can the "undocumented feature" be added as a real feature so we can have an easy way to select hifi or video sound automatically?