Beam Length override not working.

[Rodrigo Pinto]

Hello all. My first message here. 

I'm writing a guitar music and I have a problem I could not solve.

I'm using Lilypond for Windows (v2.18.2).

I tried to make a minimal example of my problem. Here is the code:

%%%%%%%%%%begin%%%%%%%%%%%%%%%%%%%%% 

\version "2.18.2"

\new Staff 

\relative c'' {

\time 2/4

  << 

{\stemUp r16 <a' c> r8 r16 <a c> r8 }

\\

{ \stemDown e8 e16 ees d8 d16 des }

\\ 

{ \stemDown c,8. c16 b8. bes16 } 

  >> 

}

%%%%%%%%%%end%%%%%%%%%%%%%%%%%%%%% 

Following the documentation on 

http://lilypond.org/doc/v2.18/Documentation/snippets/tweaks-and-overrides#tweaks-and-overrides-altering-the-length-of-beamed-stems

I modified the code trying to shorten the beam for the D notes that are ugly:

%%%%%%%%%%begin%%%%%%%%%%%%%%%%%%%%% 

\version "2.18.2"

\new Staff 

\relative c'' {

\time 2/4

  << 

{\stemUp r16 <a' c> r8 r16 <a c> r8 r16 <a c> r8 r16 <a c> r8}

\\

{ \stemDown 

e8 e16 ees  

\override Stem.details.beamed-lengths = #'(2)  

d8 d16 des 

\revert Stem.details 

e8 e16 ees d8 d16 des }

\\ 

{ \stemDown c,8. c16 b8. bes16 c8. c16 b8. bes16 } 

  >> 

}

%%%%%%%%%%end%%%%%%%%%%%%%%%%%%%%% 

But there is no change at all. I noticed that if I overding the beam length before the first E (on the same voice) it changes the beam for the E, but not for the D.

Thanks,

Rodrigo