Incorrect icons initially displayed in custom theme

[Phil Tooley]

Dear all,
I am trying to write a few custom themes and am running into a slightly odd 
problem with the icons.
It seems initially the top menuentry gets a default (tux) icon rather than the 
correct icon, but then as soon as I interact with the screen in any way, the 
icon suddenly changes to the correct one. I do not see this behaviour with 
other themes but I am deeply puzzzled as to what is incorrect about mine. Any 
hints would be greatly appreciated.
Theme: https://github.com/Telemin/grub2-gentoo-flat
Issue images: https://gist.github.com/Telemin/2d4e7c1697a711e529d34a20c26dcae9
Many Thanks
Phil Tooley