Questions about Stem #'length

[Marc Hohl]

Hi,

I tried to manipulate the length of the stems but I got strange results.
Please compile the following file:

---------------------------------------

\version "2.13.3"

test = \relative c {
 << { c4 ( d\5 ) e ( f ) } \\ g,1 >>
 << { e''4 ( f ) e ( f ) } \\ { c4 ( d ) c ( d ) } >>
 e4\1 ( f\1 ) f\1 ( e\1 )
 e\2 ( f\2 ) f\2 ( e\2 )
 e\3 ( f\3 ) f\3 ( e\3 )
 e\4 ( f\4 ) f\4 ( e\4 )
 e,\5 ( f\5 ) f\5 ( e\5 )
 e\6 ( f\6 ) f\6 ( e\6 )
 \set doubleSlurs = ##t
 < e\6 b'\5 e\4 >2 ( < f\6 c'\5 f\4 > )
}


\score { % standard behaviour
 <<
     \new Staff { \clef "G_8" \test }
     \new TabStaff <<
        \new TabVoice = "1" { s1*2 }
        \new TabVoice = "2" { s1*2 }
        \test
     >>
 >>
}

\score { % changed layout
 <<
     \new Staff { \clef "G_8" \test }
     \new TabStaff <<
        \new TabVoice = "1" { s1 }
        \new TabVoice = "2" { s1 }
        \test
     >>
 >>
 \layout {
   \context {
     \TabVoice
     \override Slur #'direction = #UP
     \override Stem #'length = #0
   }
   \context {
     \Voice
     \override Slur #'direction = #UP
     \override Stem #'length = #0
   }
   \context {
     \TabStaff
     \override NoteColumn #'ignore-collision = ##t
   }
 }
}

---------------------------------

Despite the settings for Stem #'length, some of the stems are still visible;
moreover, the slurs in the first tablature line show a strange behavior:
in the first measure, the slurs in the upper voice are attached to the 
fret numbers,
whereas the second measure has slurs attached to the stems.

Why are the stems still (partly) visible?

Thanks in advance

Marc