Accidental overlaying stem

[Nick Payne]

I think I have reported this before - a beamed note with an accidental 
on a ledger line above the stave has the accidental colliding with the 
stem of the previous note. For different notes it happens at different 
heights above the stave and also seems to depend on the length of the 
stem of the previous note:

\version "2.13.30"

\relative c' {
    \time 3/4
% \override Staff.Stem #'X-extent = #'(4 . 4)
    \stemUp ais8[ bis'' ais] ais,[ bis'! ais] ais, [ais' ais] ais, 
[ais''! ais]
}

The second png shows the effect of activating the override, but the 
override doesn't work at all for the first B# and not to the extent that 
it should for the second last A#. How can I fix the problem - for the 
first B# in particular, as that's the actual problem I encountered in 
the score I'm engraving.

Nick

test1.png
Description: PNG image

test2.png
Description: PNG image