Finally, I have solved this mystery after a long time, I could not believe how simple the fix was.
This mystery is related to the Walkman phones, where the Walkman icon would disappear from the menu.
The cause of the issue is the name of the movieclip containing the walkman icon, so to fix it simply locate the following lines "var App8_" and replace them with
var App8_IconName = "MEDIAPLAYER_DESKTOP_ICN";
var App8_Text = "walkman";
Also, make sure you rename your movieclip so it corresponds to the new icon name "MEDIAPLAYER_DESKTOP_ICN"
Now simply test your menu and it should now work