if it had an icon tag and no icon_size tag, the game wouldn't let it load.
I looked at the file in question, and true enough, it has no icon_size tag... because it doesn't need one, it has an icons= tag, where the icon_size is on each icon of the icons table.
If someone else (Omni in this case as you said) decides to change the icon, it's their responsibility to make sure they set the icon_size correctly.
A lesson I learned myself when changing an icon in a different mod, and someone else updated it to set a different sized icon. it would error because the icon_size was wrong. so in short, if you set an icon, always set an icon_size too, otherwise you get errors. Icons is a strange exception, you can define an icons table without icon sizes, but I think then you still need icon_size on the main item that has an icons table.
