I'm Stumped

[Lyle Raymond]

I'd like you guys' input on a couple of difficulties I'm having with my first 
jazz lead sheet.  The source code is included below.  First, however, my 
questions:

1.  While rendering, Lilypond reports: "programming error: round filled box 
vertical extent smaller than blot; decreasing blot (Continuing; cross 
thumbs)."  What does this mean?  

2.  Perhaps related to the first question:  After rendering, chord slashes 
appear to have a little tail.  How do I get rid of it?

3.  How can I include a transposed series of lead sheet chords above the 
second of the two staves?

4.  Finally, if anyone is willing to critique my overall form and syntax I'd 
greatly appreciate it.  It is my guess that a lack of knowledge of Lilypond 
syntax is causing my difficulties.  Furthermore, any hints regarding 
optimization and legibility would be very welcome.

Here's the score (piece copyright 2003, S. Lyle Raymond):

        %% MONKEYSTUMP, THE DRIFTER %%
        %% S. Lyle Raymond, composer %%

\header {
        title = "Monkeystump, the Drifter"
        composer = "S L Raymond"
        pagenumber = "no"
        tagline = " "
        }
\score {

        \notes
        <<
        \context ChordNames \chords {r1 d:7 r r r c:7 r r b:9+ a:7 g:7 f:7 es:7}
        \new Staff \relative d'' {
                \property Staff.instrument = #"Tenor Sax"
                \key d \major
                \time 4/4
                \clef treble
                \skip 2
                a8 c e d
                \repeat volta 2 {
                        r1
                        r2 r4 b'4
                        c8 dis,8 e g b a r8 fis
                        r8 g,4. bes4 d8 c~
                        c1
                        r2 r8 e8 g a
                        bes a g f e d r8 g~
                        g4 r4 d8 c b a
                        r8
                        \property Voice.TextScript\override #'padding = #2.5
                        a_\markup "Last Time: repeat final 4 bars" b c cis a' 
aes g~
                        g2 b,8 d g f~
                        f1~
                        f1
                        }
                }
        \new Staff{
                \property Staff.instrument = #"Bass"
                \key c \major
                \clef bass
                \skip 2
                r2 
                        r8 c4.^\accent~ c2~
                        c1~
                        c1~
                        c2 r2
                
                        r4. bes,8^\accent~ bes,2~
                        bes,1~
                        bes,1
                        a,2
                \property Voice.NoteHead \override #'style = #'slash
          \property Voice.Stem \override #'length = #0 d4 d
                        d d d d
                        d d d d
                        d d d d
                        d d d d
                \property Voice.NoteHead \revert #'style
         \property Voice.Stem \revert #'length
        }
        >>
        \paper {}
        }