BarLines behave weirdly when colored

[Valentin Petzel]

Hello you all,

on SE I’ve encountered a weird issue: BarLine stencils in Lilypond do not have 
rounded corners, but they are shortened by half a staff line, so the rounded 
ends of the staff lines lead to some rounded effect for the last bar line. But 
when changing the color of the BarLine it will instead take the whole height.

Thus I want to ask:
1) Does anyone have an idea why this could be happening?
2) Is there some intention in this happening or can this be considered a bug?
3) Is there a reason why this BarLine is shortened in the first place (if we 
want rounded corners we could always draw the Bar Lines with rounded corners)?

Here is an example:

\version "2.23"

\paper {
  indent = 0
  ragged-right = ##t
  system-system-spacing = #'((basic-distance . 6))
}

{
  \omit Staff.Clef
  \omit Staff.TimeSignature
  \override TextScript.Y-offset = #self-alignment-interface::y-aligned-on-self
  \override TextScript.self-alignment-Y = #0
  \textLengthOn
  s16 \bar "|" 
  \stopStaff
  s^"This BarLine is slightly shorter and thus rounded"
  \startStaff\bar ""
  \break
  s \once\override Staff.BarLine.color = #red \bar "|" 
  \stopStaff
  s^"This BarLine is slightly of full length, thus straight"
  \bar ""\break
  
  \omit Score.StaffSymbol
  \startStaff
  s16 \bar "|" 
  s16
  \once\override Staff.BarLine.extra-offset = #'(-5.32 . 0)
  \once\override Staff.BarLine.color = #red \bar "|"
  \once\override TextScript.extra-offset = #'(-5.32 . 0)
  s^"Next to each other this difference in length can be seen quite clearly"
}


Cheers,
Valentin

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