Stem.stem-begin-position not giving desired output on beamed stems (tablature)

[Carl Williams]

Hi Everyone, 

First time using a mailing list. 
I've raked through the documentation pages all today and yesterday (and learnt 
a lot), but still couldn't solve this. 

So I want to create (ukulele) tablature where all the stems and beams are above 
the staff. 
I use the \override Stem.stem-begin-position to set the unbeamed stems above, 
but I think it aught to affect the beamed stems too (they are stems too after 
all!). bug?

Does anyone know any workarounds? 
I've tried lots of things. I think it could be done if somehow the stems were 
'un-parented' from the noteheads in the Y-direction, and then parented to 
something else in the Y-direction (can a grob have 2 parents?). I haven't bee 
able to do this though. 

Here's the example: 
\version "2.18.2"

\new TabStaff \with {
  stringTunings = #ukulele-tuning
} {
  %set bottom of stem position
  \override Stem.stem-begin-position = #4.5
  %set stem length
  \override Stem.length = #5
  %set top of beam position
  \override Beam.positions = #'(4.6 . 4.6)
  \stemUp
  \relative c' {
    \tabFullNotation
    r8 g'\4 c,4 e2 |
    a1 |
    g8\4 c, e a c,[ c] a'8 a |
  }
}

There's an SVG attached, not sure what the deal is with pictures. 

Eventually I want to look at half length stems for minim and quarter length for 
semibreve, but one thing at a time. 

Thanks, 
Carl

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