30. Switching a track in Ableton Live does not open the last MP Host

When you have the option to auto-hide plugins in Ableton Live, 

switching a track hides the small window of the MP Host while the controller window remains open and you can still control the plugin. This is often a benefit because you can still control a plugin located on another track (while without the MP Controller you cannot do that, unless you change the A.L. option.)

When you change a track and you choose to control another plugin via the MP Host, it will close the previous MPH Controller window from the previous track. 

Navigating back to the previous track requires that you press on the Control & Display button (the controller icon on the small window) because Ableton does not notify plugins when a track has switched.

If you don't want to use the mouse, a good practice is to drag beforehand the small window of the MP Host on the controller's touch screen. 

Once you change a track, touch the Control and Display (Controller Icon on the single host). 

Then touch the touchscreen or click anywhere on the controller window, the small window will be hidden below the big window.

Thereafter, when you switch a track again in Ableton the small window will show on top.

The same applies to the MP Multi Host.

After changing a track, Touch the Control and Display (Controller Icon on the single host) 

The MP Host will automatically open the controller window when the MP Host plugin opens from the DAW. This means that the MPH plugin is completely closed in Ableton Live and you click on the A.L. icon to open it In other words, opening the small window will automatically open the controller window as well.

Alternatively, If you have another midi controller to open/close plugins in Ableton, like Push or other midi controller, you can program it to close the MP Host and then open it, and it will automatically open the controller window.