To restore the hiding function, just do the following...
1. Right click on an empty part of the Taskbar
2. From the popup menu select 'Properties'
3. The 'Taskbar and Start Menu Properties' window will open.
4. Now click the 'Customize...' button
5. The 'Customize Notifications' window will open.
6. In the column 'Behavior' set each one to 'Always hide' (you only need to do this for the Current Items not the Past Items)
7. Now click 'OK'
8. The window will close, all your icons will be hidden, and the chevron button will appear again.
9. Now click 'Customize' again and restore all your icon settings to what they were before, or whatever you prefer.
10. Click 'OK' again to close the window.
11. Click 'OK' to close the last window.