Why does removing Bar_engraver also removes clef?

[Gez]

I know this has been written about on the list before but the 
documentation has changed since then (I've checked pretty thoroughly).

I'm looking for a way to write a load of short free-form pieces with 
automatic line breaks (so candenzaOn is not useful since it requires 
manual breaks).  I'd like to inhibit the Bar_engraver in all the pieces 
in one book/ly file, rather than write an override in each melody.  So 
far the workaround I've found uses a variable with override that I do 
have to insert in each score, but at least I can use the variable for 
other purposes as well.

My minimal examples here show various scenarios I tried.   If someone 
can confirm that it's all working as it's supposed to, then that's good 
to know, but I'd be really grateful if someone can also point me to 
where the documentation explains why removing the the Bar_engraver also 
removes the Clefs.

Many thanks,
Gez

****************************************************
\version "2.18.0"


thistest = {
\override Staff.BarLine.stencil = ##f
}

 \score {
   \relative c'{
   \thistest
  \repeat unfold 40 { c1 }
  }
 \header {
 piece = "Using variable override stencil keeps clef engraved with 
automatic breaks"
 }
 }

   \score {
  \relative c'{
     \cadenzaOn
   \repeat unfold 40 { c1 }
  }
   \header {
 piece = "Using cadenzaOn with no breaks sends line off edge of page"
 }
  }


  \score {
   \relative c'{
     \cadenzaOn
   c c c c \break c c c c
  }
   \header {
 piece = "Using cadenzaOn and break alone does not break the line"
 }
 }


  \score {
  \relative c'{
     \cadenzaOn
   c c c c \bar "" \break c c c c
  }
   \header {
 piece = "Using cadenzaOn with break after invisible bar does break 
line and engrave clef"
 }
  }




  \score {
          \layout  {
   \context { \Staff \remove Bar_engraver }
 }
   \relative c'{
  \repeat unfold 40 { c1 }
  }
  \header {
 piece = "Removing bar engraver creates automatic break but no clef is 
engraved"
 }
  }


 \score {
         \layout  {
   \context { \Staff \remove Bar_engraver }
 }
\relative c'{
   c c c c \break c c c c
  }
   \header {
 piece = "Removing bar engraver also removes Clef even at added break"
 }
 }

  \score {
      \layout  {
   \context { \Staff \remove Bar_engraver }
 }
 \relative c'{
   c c c c \bar "" \break c c c c
  }
   \header {
 piece = "Removing bar engraver also removes Clef even at added 
invisible bar plus break"
 }
  }

***************************************************************