Is this metamethod __isdef bug?

["actboy168" <actboy168@...>]

This is the test code.

> local mt = {}

> function mt:__isdef()

> return true

> end

> local t = setmetatable({}, mt)

> print(t.a == undef)

And the output is:

> >>lua test.lua

> lua: test.lua:6: attempt to call a boolean value (global 'print')

> stack traceback:

>         test.lua:6: in main chunk

>         [C]: in ?

-- actboy168