Is this a bug in secure frames SetFrameRef/GetFrameRef?

[Duugu]

I've found some strange behavior within the Set/GetFrameRef() thing for secure frames.

Consider the following code:

local header = CreateFrame("Frame", "testheader", UIParent, "SecureHandlerStateTemplate")
header:SetFrameRef("ActionButton1", _G["ActionButton1"]) 
 
local button = CreateFrame("CheckButton", "testbutton1", header, "SecureActionButtonTemplate, ActionButtonTemplate")
button:SetPoint("CENTER", UIParent, "CENTER")
    
header:WrapScript(button, "OnClick", [[
    print("ActionButton1.IsForbidden =", self:GetParent():GetFrameRef("ActionButton1").IsForbidden)
]])
 
print("ActionButton1.IsForbidden =", _G["ActionButton1"].IsForbidden, _G["ActionButton1"]:IsForbidden())

It prints:

ActionButton1.IsForbidden = function: <.....> false

Now click the test button.

It prints:

ActionButton1.IsForbidden = nil

Ehm?

Try again:

print("ActionButton1.IsForbidden =", _G["ActionButton1"].IsForbidden, _G["ActionButton1"]:IsForbidden())

Result:

ActionButton1.IsForbidden = function: <.....> false

WTF??

So, is it me, or is GetFrameRef() returning something that is not equal to the original object that was passed to SetFrameRef()?
Could someone please verify if this is a bug or if I'm just stupid?