Mystery of the Disappearing X

[Malsomnus]

My add-on has this frame which has a little X in the corner to close it.
The frame shows automatically on login.
When I just login, everything's fine. When I /reload, however, the X does not show. It's there, it's clickable, it works, but it's invisible.
I can make it visible again by changing its text.
Does anybody have any idea what the hell?

f.btnX = CreateFrame ("EditBox", nil, f)
f.btnX:SetPoint ("TOPRIGHT", f, "TOPRIGHT")
f.btnX:SetSize (10,12)
f.btnX:SetTextColor (1.0,0.77,0.27,1.0)
f.btnX:SetTextInsets (0, 0, 2, 2)
f.btnX:SetFont ("Fonts\\FRIZQT__.TTF", 11)
f.btnX:SetAutoFocus (false)
f.btnX:Disable ()
f.btnX:SetText ('x')
f.btnX:SetScript ("OnMouseDown", function (self, button)
    f:Hide ()
end)