Direction of tuplet bracket and number depends on length of rest

[Henning]

When there are two eights rests and one eigth note in one triplet
the direction of the triplet bracket and the triplet number is not
as expected. I would expect it on the stem side.
 
With a quarter rest instead of 2 eights rests everything is normal.
 
This happens only with stems up.
 
Is this a known bug if it is a bug at all?
 
------8<-----------------------
 
\version "2.13.59"
 
\markup {
  change of direction with stems up
}
{
  \times 2/3 { a'8 r8 r8  }
  \times 2/3 { a'8 r4     }
  \times 2/3 { r8  r8 a'8 }
  \times 2/3 { r4     a'8 }
}
\markup {
  no change of direction with stems down
}
{
  \times 2/3 { b'8 r8 r8  }
  \times 2/3 { b'8 r4     }
  \times 2/3 { r8  r8 b'8 }
  \times 2/3 { r4     b'8 }
}