synchronization of feathered beams

[Stefan Thomas]

Dear community,
I have a problem with the synchronisation in the below quoted snippet.
I expect to have the notes on the end of the bar on the same vertical height.
How can I achieve it?
Thanks for help,
Stefan

\version "2.12.3"
global = { \time 7/8 }
upper = { \global 
   \featherDurations #(ly:make-moment 1 2)
 { des''8 -. [\p\< es''8 -. e''8 -. f''8 -. ges''8 -. as''8 -. c'''8 -> -. \f] } 
}
lower = { \global
   \featherDurations #(ly:make-moment 1 2)
 { r2 r4   <fis'' c'''>8 -> -. \sfz }
}
\score {
  << \new Staff \upper
    \new Staff \lower >>
}