Odd slur placement/collisions with stems and flags

[Bryan Previte]

% On stem-down/stem-up patterns, the slurs are placed oddly and occasionally
% collide with the stems and flags of the stem-down notes.

\new Staff {
        \time 2/4
        \key g \major
        \clef treble
        \relative c' {  
                \context Voice = "melodyVoi" {  
                        \partial 8
                        \repeat "unfold" 4 { d8 g8 (b4) }
                        \repeat "unfold" 4 { d,8 a'8 (c4) } \bar "|."
                }
        }
}
\version "2.13.54"