The symbol or picture is being set by the Visual Scene.
To get your symbols to "stick", go to the dashboard and levels menu and change the Topics to Visual scene. Apply and go back to the master page. Now visit the topic page and edit the visual scene with the symbol or picture you would like. Go back to the master page and then back to the dashboard and levels, change Topics back to the grid view.
To get your symbols to "stick", go to the dashboard and levels menu and change the Topics to Visual scene. Apply and go back to the master page. Now visit the topic page and edit the visual scene with the symbol or picture you would like. Go back to the master page and then back to the dashboard and levels, change Topics back to the grid view.