[Duugu]

I just tried this with my lvl 13 shaman (don't has windfury right now):

hooksecurefunc('TemporaryEnchantFrame_Update', function(self,...)
    local a = GetSpellTexture(8232) --(windfury)
    TempEnchant1Icon:SetTexture(a)
end)

Result: texture is 'empty' (means GetTexture() returns the correct path but the texture is not visible).

So I tried

hooksecurefunc('TemporaryEnchantFrame_Update', function(self,...)
    local a = GetSpellTexture(8024) --(Flametongue)
    TempEnchant1Icon:SetTexture(a)
end)

Shows the texture as expected. (lvl 14 shaman has Flametongue)

Then I tried

hooksecurefunc('TemporaryEnchantFrame_Update', function(self,...)
    local a = GetSpellTexture(8232) --windfury
    ActionButton1Icon:SetTexture(a)
    TempEnchant1Icon:SetTexture(a)
end)

(I know its senseless ... just to see what would happen)

Result: TempEnchant1Icon shows the windfury texture.