loose stemlet-is this a bug?

[Mehmet Okonsar]

Hello users and creators of the best music notation program in the world!
here is an except from a score I'm working on:
there seems to be a loose stemlet hanging at the left hand part just
before the \changeStaff
-------------------------START CODE
\version "2.7.27"
\include "english.ly" 

forceAlterations =
  #(def-music-function (parser location music) (ly:music?)
     (music-map (lambda (m)
                  (if (eqv? (ly:music-property m 'name) 'NoteEvent)
                      (set! (ly:music-property m 'force-accidental) #t))
                  m)
                music)
     music)

\score{

\forceAlterations {


\new PianoStaff {
\time 4/4
<<
\context Staff = "RH" {  
<<
    {
        \once\override DynamicText #'extra-offset = #'(-6 . -2.5)
        <b, c e fs gs>4\pp
        \clef treble
        s4
        \clef bass
        \once\override DynamicText #'extra-offset = #'(-3 . -2.5)
        <b, c e fs gs>4\p
        \clef treble
        s8 s16
        \hideNotes %this is to tie that to next note in another voice..
        <ds' cs''>16~
        \unHideNotes
    }
\\
    {
        s1
    }
>>
}
%=====================================================================
\context Staff = "LH" {  
\clef bass
\slurUp
\stemUp
\acciaccatura { g,8} <a,, bf,,d, fs,>4
\once\override DynamicText #'extra-offset = #'(-4 . 4)
\once\override Hairpin #'extra-offset = #'(0 . 6)
cs,,32\<\pp
\change Staff=RH
\once\override DynamicText #'extra-offset = #'(-4.5 . 30)
ds''''32\pp
<f' b'>8.->\!
\change Staff=LH
\slurUp
\stemUp
\acciaccatura { g,8} <a,, bf,,d, fs,>4
\once\override DynamicText #'extra-offset = #'(-4 . 4)
cs,,32\pp
\change Staff=RH
\once\override DynamicText #'extra-offset = #'(-4.5 . 12)
ds''''32\pp
<f b f'>8->
\once\override DynamicText #'extra-offset = #'(-3 . 11)
<ds' cs''>16\p
}
>>
}%=====================================================================

}
}
\layout {
    raggedright = ##t
    \context {
        \Staff
            \remove "Time_signature_engraver"
    }
}
-------------------------------------END CODE


------------- 
Best regards,
Mehmet Okonşar, pianist-composer
www.okonsar.com
address@hidden