BUG: ``E685: Internal error: func_unref()'' when using delfunction on local function varible containing a dictionary function

[ZyX]

Attached script causes a error when sourced using
    vim -u NONE -c 'set nocompatible' -c 'so ~/tmp/vim/test-bug.vim
Error message:
    Error detected while processing /home/zyx/tmp/vim/test-bug.vim:
    line    8:
    E685: Internal error: func_unref()
    E685: Internal error: func_unref()
Tested on vim-7.2.442 and vim-7.3 revision 
2493:ed997d0ceb2674b8fb3d707130647197c5cf8f83.

function! GetFunction()
    let r={}
    execute      "function r.f()\n".
                \"endfunction"
    let F=r.f
    delfunction F
endfunction
call GetFunction()

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