something strange with tuplets

[Adam Good]

Hi, I'm getting strange results when trying to make a tuplet grouping...
the piece is in 12/8
i want four 16th notes within three 8th notes

in the example below i have 2 staves.
1. the top is showing the proper rhythm and proper grouping of 8th 
notes.
2. bottom is a mirror of the above except i want to cram four 16th 
notes into the first three 8th notes of bar 1.

but you can see how the barline is getting shoved over to the wrong 
place. it's interpreting two 16th notes as a full 8th notes for some 
reason?

---

\relative
  \new Staff { \key c \major

 #(revert-auto-beam-setting '(end * * 12 8) 3 8)
 #(revert-auto-beam-setting '(end * * 12 8) 3 4)
 #(revert-auto-beam-setting '(end * * 12 8) 9 8)

#(override-auto-beam-setting '(end 1 8 12 8) 3 8)
#(override-auto-beam-setting '(end 1 8 12 8) 7 8)
#(override-auto-beam-setting '(end 1 8 12 8) 10 8)

  \key e \minor
  \time 12/8

\repeat volta 2 { \mark \default
c'8 d e d c b g a4. d,4 | c'4 b8 c d b g a4. a4 |
c8 d e d c b g a4. d,4 | c'4 b8 c d b g a4. a4 } \break

\repeat volta 2 { \mark \default
\set tupletNumberFormatFunction = #fraction-tuplet-formatter
\times 3/4 {b16 c d e} d8 c b g a4. d,4 | c'4 b8 c d b g a4. a4 |
c8 d e d c b g a4. d,4 | c'4 b8 c d b g a4. a4 } \break

}

\version "2.8.1"  % necessary for upgrading to future LilyPond versions.