Open the local procedure UI_LoadTasks from the MNU_ERPw page.
Find the line:
TreeAdd(Sidebar_TreeView_Inventory,"Lists"+TAB+"Products",tvDefault,"PGB_Products",tvLast)
and add a second tvDefault [after the first one].
Line should be like this now:
TreeAdd(Sidebar_TreeView_Inventory,"Lists"+TAB+"Products",tvDefault,tvDefault,"PGB_Products",tvLast)