whiteout of beam doesn't work

[Stefan Thomas]

Dear community,
in the following snippet, I wanted to white out the beam.
Unfortunately it doesn't work and I don't understand the reason for it.
Any idea?

\version "2.14.2"
Music = \relative c''' {
  \override Staff.TimeSignature #'whiteout = ##t
    \override TimeSignature #'layer = #3
     \override Staff.StaffSymbol #'layer = #4
     \override Staff.Beam #'layer = #2 % why isn't the beam transparent, when the time-signature change appears?
  \time 2/4 
  d8[ f e] \once \override Beam #'positions = #(cons 1 1) d[
  \time 5/8
  f] d[ e] r4
}

\new Staff \Music